Search moodle.org's
Developer Documentation

See Release Notes

  • Bug fixes for general core bugs in 4.0.x will end 8 May 2023 (12 months).
  • Bug fixes for security issues in 4.0.x will end 13 November 2023 (18 months).
  • PHP version: minimum PHP 7.3.0 Note: the minimum PHP version has increased since Moodle 3.10. PHP 7.4.x is also supported.

Differences Between: [Versions 310 and 400] [Versions 39 and 400] [Versions 400 and 401] [Versions 400 and 402] [Versions 400 and 403]

   1  <?php
   2  // This file is part of Moodle - http://moodle.org/
   3  //
   4  // Moodle is free software: you can redistribute it and/or modify
   5  // it under the terms of the GNU General Public License as published by
   6  // the Free Software Foundation, either version 3 of the License, or
   7  // (at your option) any later version.
   8  //
   9  // Moodle is distributed in the hope that it will be useful,
  10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  // GNU General Public License for more details.
  13  //
  14  // You should have received a copy of the GNU General Public License
  15  // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16  
  17  /**
  18   * Abstract database driver class.
  19   *
  20   * @package    core_dml
  21   * @copyright  2008 Petr Skoda (http://skodak.org)
  22   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  23   */
  24  
  25  defined('MOODLE_INTERNAL') || die();
  26  
  27  require_once (__DIR__.'/database_column_info.php');
  28  require_once (__DIR__.'/moodle_recordset.php');
  29  require_once (__DIR__.'/moodle_transaction.php');
  30  
  31  /** SQL_PARAMS_NAMED - Bitmask, indicates :name type parameters are supported by db backend. */
  32  define('SQL_PARAMS_NAMED', 1);
  33  
  34  /** SQL_PARAMS_QM - Bitmask, indicates ? type parameters are supported by db backend. */
  35  define('SQL_PARAMS_QM', 2);
  36  
  37  /** SQL_PARAMS_DOLLAR - Bitmask, indicates $1, $2, ... type parameters are supported by db backend. */
  38  define('SQL_PARAMS_DOLLAR', 4);
  39  
  40  /** SQL_QUERY_SELECT - Normal select query, reading only. */
  41  define('SQL_QUERY_SELECT', 1);
  42  
  43  /** SQL_QUERY_INSERT - Insert select query, writing. */
  44  define('SQL_QUERY_INSERT', 2);
  45  
  46  /** SQL_QUERY_UPDATE - Update select query, writing. */
  47  define('SQL_QUERY_UPDATE', 3);
  48  
  49  /** SQL_QUERY_STRUCTURE - Query changing db structure, writing. */
  50  define('SQL_QUERY_STRUCTURE', 4);
  51  
  52  /** SQL_QUERY_AUX - Auxiliary query done by driver, setting connection config, getting table info, etc. */
  53  define('SQL_QUERY_AUX', 5);
  54  
  55  /**
  56   * Abstract class representing moodle database interface.
  57   * @link http://docs.moodle.org/dev/DML_functions
  58   *
  59   * @package    core_dml
  60   * @copyright  2008 Petr Skoda (http://skodak.org)
  61   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  62   */
  63  abstract class moodle_database {
  64  
  65      /** @var database_manager db manager which allows db structure modifications. */
  66      protected $database_manager;
  67      /** @var moodle_temptables temptables manager to provide cross-db support for temp tables. */
  68      protected $temptables;
  69      /** @var array Cache of table info. */
  70      protected $tables  = null;
  71  
  72      // db connection options
  73      /** @var string db host name. */
  74      protected $dbhost;
  75      /** @var string db host user. */
  76      protected $dbuser;
  77      /** @var string db host password. */
  78      protected $dbpass;
  79      /** @var string db name. */
  80      protected $dbname;
  81      /** @var string Prefix added to table names. */
  82      protected $prefix;
  83  
  84      /** @var array Database or driver specific options, such as sockets or TCP/IP db connections. */
  85      protected $dboptions;
  86  
  87      /** @var bool True means non-moodle external database used.*/
  88      protected $external;
  89  
  90      /** @var int The database reads (performance counter).*/
  91      protected $reads = 0;
  92      /** @var int The database writes (performance counter).*/
  93      protected $writes = 0;
  94      /** @var float Time queries took to finish, seconds with microseconds.*/
  95      protected $queriestime = 0;
  96  
  97      /** @var int Debug level. */
  98      protected $debug  = 0;
  99  
 100      /** @var string Last used query sql. */
 101      protected $last_sql;
 102      /** @var array Last query parameters. */
 103      protected $last_params;
 104      /** @var int Last query type. */
 105      protected $last_type;
 106      /** @var string Last extra info. */
 107      protected $last_extrainfo;
 108      /** @var float Last time in seconds with millisecond precision. */
 109      protected $last_time;
 110      /** @var bool Flag indicating logging of query in progress. This helps prevent infinite loops. */
 111      protected $loggingquery = false;
 112  
 113      /** @var bool True if the db is used for db sessions. */
 114      protected $used_for_db_sessions = false;
 115  
 116      /** @var array Array containing open transactions. */
 117      protected $transactions = array();
 118      /** @var bool Flag used to force rollback of all current transactions. */
 119      private $force_rollback = false;
 120  
 121      /** @var string MD5 of settings used for connection. Used by MUC as an identifier. */
 122      private $settingshash;
 123  
 124      /** @var cache_application for column info */
 125      protected $metacache;
 126  
 127      /** @var cache_request for column info on temp tables */
 128      protected $metacachetemp;
 129  
 130      /** @var bool flag marking database instance as disposed */
 131      protected $disposed;
 132  
 133      /**
 134       * @var int internal temporary variable used to fix params. Its used by {@link _fix_sql_params_dollar_callback()}.
 135       */
 136      private $fix_sql_params_i;
 137      /**
 138       * @var int internal temporary variable used to guarantee unique parameters in each request. Its used by {@link get_in_or_equal()}.
 139       */
 140      protected $inorequaluniqueindex = 1;
 141  
 142      /**
 143       * @var boolean variable use to temporarily disable logging.
 144       */
 145      protected $skiplogging = false;
 146  
 147      /**
 148       * Constructor - Instantiates the database, specifying if it's external (connect to other systems) or not (Moodle DB).
 149       *              Note that this affects the decision of whether prefix checks must be performed or not.
 150       * @param bool $external True means that an external database is used.
 151       */
 152      public function __construct($external=false) {
 153          $this->external  = $external;
 154      }
 155  
 156      /**
 157       * Destructor - cleans up and flushes everything needed.
 158       */
 159      public function __destruct() {
 160          $this->dispose();
 161      }
 162  
 163      /**
 164       * Detects if all needed PHP stuff are installed for DB connectivity.
 165       * Note: can be used before connect()
 166       * @return mixed True if requirements are met, otherwise a string if something isn't installed.
 167       */
 168      public abstract function driver_installed();
 169  
 170      /**
 171       * Returns database table prefix
 172       * Note: can be used before connect()
 173       * @return string The prefix used in the database.
 174       */
 175      public function get_prefix() {
 176          return $this->prefix;
 177      }
 178  
 179      /**
 180       * Loads and returns a database instance with the specified type and library.
 181       *
 182       * The loaded class is within lib/dml directory and of the form: $type.'_'.$library.'_moodle_database'
 183       *
 184       * @param string $type Database driver's type. (eg: mysqli, pgsql, mssql, sqldrv, oci, etc.)
 185       * @param string $library Database driver's library (native, pdo, etc.)
 186       * @param bool $external True if this is an external database.
 187       * @return moodle_database driver object or null if error, for example of driver object see {@link mysqli_native_moodle_database}
 188       */
 189      public static function get_driver_instance($type, $library, $external = false) {
 190          global $CFG;
 191  
 192          $classname = $type.'_'.$library.'_moodle_database';
 193          $libfile   = "$CFG->libdir/dml/$classname.php";
 194  
 195          if (!file_exists($libfile)) {
 196              return null;
 197          }
 198  
 199          require_once($libfile);
 200          return new $classname($external);
 201      }
 202  
 203      /**
 204       * Returns the database vendor.
 205       * Note: can be used before connect()
 206       * @return string The db vendor name, usually the same as db family name.
 207       */
 208      public function get_dbvendor() {
 209          return $this->get_dbfamily();
 210      }
 211  
 212      /**
 213       * Returns the database family type. (This sort of describes the SQL 'dialect')
 214       * Note: can be used before connect()
 215       * @return string The db family name (mysql, postgres, mssql, oracle, etc.)
 216       */
 217      public abstract function get_dbfamily();
 218  
 219      /**
 220       * Returns a more specific database driver type
 221       * Note: can be used before connect()
 222       * @return string The db type mysqli, pgsql, oci, mssql, sqlsrv
 223       */
 224      protected abstract function get_dbtype();
 225  
 226      /**
 227       * Returns the general database library name
 228       * Note: can be used before connect()
 229       * @return string The db library type -  pdo, native etc.
 230       */
 231      protected abstract function get_dblibrary();
 232  
 233      /**
 234       * Returns the localised database type name
 235       * Note: can be used before connect()
 236       * @return string
 237       */
 238      public abstract function get_name();
 239  
 240      /**
 241       * Returns the localised database configuration help.
 242       * Note: can be used before connect()
 243       * @return string
 244       */
 245      public abstract function get_configuration_help();
 246  
 247      /**
 248       * Returns the localised database description
 249       * Note: can be used before connect()
 250       * @deprecated since 2.6
 251       * @return string
 252       */
 253      public function get_configuration_hints() {
 254          debugging('$DB->get_configuration_hints() method is deprecated, use $DB->get_configuration_help() instead');
 255          return $this->get_configuration_help();
 256      }
 257  
 258      /**
 259       * Returns the db related part of config.php
 260       * @return stdClass
 261       */
 262      public function export_dbconfig() {
 263          $cfg = new stdClass();
 264          $cfg->dbtype    = $this->get_dbtype();
 265          $cfg->dblibrary = $this->get_dblibrary();
 266          $cfg->dbhost    = $this->dbhost;
 267          $cfg->dbname    = $this->dbname;
 268          $cfg->dbuser    = $this->dbuser;
 269          $cfg->dbpass    = $this->dbpass;
 270          $cfg->prefix    = $this->prefix;
 271          if ($this->dboptions) {
 272              $cfg->dboptions = $this->dboptions;
 273          }
 274  
 275          return $cfg;
 276      }
 277  
 278      /**
 279       * Diagnose database and tables, this function is used
 280       * to verify database and driver settings, db engine types, etc.
 281       *
 282       * @return string null means everything ok, string means problem found.
 283       */
 284      public function diagnose() {
 285          return null;
 286      }
 287  
 288      /**
 289       * Connects to the database.
 290       * Must be called before other methods.
 291       * @param string $dbhost The database host.
 292       * @param string $dbuser The database user to connect as.
 293       * @param string $dbpass The password to use when connecting to the database.
 294       * @param string $dbname The name of the database being connected to.
 295       * @param mixed $prefix string means moodle db prefix, false used for external databases where prefix not used
 296       * @param array $dboptions driver specific options
 297       * @return bool true
 298       * @throws dml_connection_exception if error
 299       */
 300      public abstract function connect($dbhost, $dbuser, $dbpass, $dbname, $prefix, array $dboptions=null);
 301  
 302      /**
 303       * Store various database settings
 304       * @param string $dbhost The database host.
 305       * @param string $dbuser The database user to connect as.
 306       * @param string $dbpass The password to use when connecting to the database.
 307       * @param string $dbname The name of the database being connected to.
 308       * @param mixed $prefix string means moodle db prefix, false used for external databases where prefix not used
 309       * @param array $dboptions driver specific options
 310       * @return void
 311       */
 312      protected function store_settings($dbhost, $dbuser, $dbpass, $dbname, $prefix, array $dboptions=null) {
 313          $this->dbhost    = $dbhost;
 314          $this->dbuser    = $dbuser;
 315          $this->dbpass    = $dbpass;
 316          $this->dbname    = $dbname;
 317          $this->prefix    = $prefix;
 318          $this->dboptions = (array)$dboptions;
 319      }
 320  
 321      /**
 322       * Returns a hash for the settings used during connection.
 323       *
 324       * If not already requested it is generated and stored in a private property.
 325       *
 326       * @return string
 327       */
 328      protected function get_settings_hash() {
 329          if (empty($this->settingshash)) {
 330              $this->settingshash = md5($this->dbhost . $this->dbuser . $this->dbname . $this->prefix);
 331          }
 332          return $this->settingshash;
 333      }
 334  
 335      /**
 336       * Handle the creation and caching of the databasemeta information for all databases.
 337       *
 338       * @return cache_application The databasemeta cachestore to complete operations on.
 339       */
 340      protected function get_metacache() {
 341          if (!isset($this->metacache)) {
 342              $properties = array('dbfamily' => $this->get_dbfamily(), 'settings' => $this->get_settings_hash());
 343              $this->metacache = cache::make('core', 'databasemeta', $properties);
 344          }
 345          return $this->metacache;
 346      }
 347  
 348      /**
 349       * Handle the creation and caching of the temporary tables.
 350       *
 351       * @return cache_application The temp_tables cachestore to complete operations on.
 352       */
 353      protected function get_temp_tables_cache() {
 354          if (!isset($this->metacachetemp)) {
 355              // Using connection data to prevent collisions when using the same temp table name with different db connections.
 356              $properties = array('dbfamily' => $this->get_dbfamily(), 'settings' => $this->get_settings_hash());
 357              $this->metacachetemp = cache::make('core', 'temp_tables', $properties);
 358          }
 359          return $this->metacachetemp;
 360      }
 361  
 362      /**
 363       * Attempt to create the database
 364       * @param string $dbhost The database host.
 365       * @param string $dbuser The database user to connect as.
 366       * @param string $dbpass The password to use when connecting to the database.
 367       * @param string $dbname The name of the database being connected to.
 368       * @param array $dboptions An array of optional database options (eg: dbport)
 369       *
 370       * @return bool success True for successful connection. False otherwise.
 371       */
 372      public function create_database($dbhost, $dbuser, $dbpass, $dbname, array $dboptions=null) {
 373          return false;
 374      }
 375  
 376      /**
 377       * Returns transaction trace for debugging purposes.
 378       * @private to be used by core only
 379       * @return array or null if not in transaction.
 380       */
 381      public function get_transaction_start_backtrace() {
 382          if (!$this->transactions) {
 383              return null;
 384          }
 385          $lowesttransaction = end($this->transactions);
 386          return $lowesttransaction->get_backtrace();
 387      }
 388  
 389      /**
 390       * Closes the database connection and releases all resources
 391       * and memory (especially circular memory references).
 392       * Do NOT use connect() again, create a new instance if needed.
 393       * @return void
 394       */
 395      public function dispose() {
 396          if ($this->disposed) {
 397              return;
 398          }
 399          $this->disposed = true;
 400          if ($this->transactions) {
 401              $this->force_transaction_rollback();
 402          }
 403  
 404          if ($this->temptables) {
 405              $this->temptables->dispose();
 406              $this->temptables = null;
 407          }
 408          if ($this->database_manager) {
 409              $this->database_manager->dispose();
 410              $this->database_manager = null;
 411          }
 412          $this->tables  = null;
 413      }
 414  
 415      /**
 416       * This should be called before each db query.
 417       * @param string $sql The query string.
 418       * @param array|null $params An array of parameters.
 419       * @param int $type The type of query. ( SQL_QUERY_SELECT | SQL_QUERY_AUX | SQL_QUERY_INSERT | SQL_QUERY_UPDATE | SQL_QUERY_STRUCTURE )
 420       * @param mixed $extrainfo This is here for any driver specific extra information.
 421       * @return void
 422       */
 423      protected function query_start($sql, ?array $params, $type, $extrainfo=null) {
 424          if ($this->loggingquery) {
 425              return;
 426          }
 427          $this->last_sql       = $sql;
 428          $this->last_params    = $params;
 429          $this->last_type      = $type;
 430          $this->last_extrainfo = $extrainfo;
 431          $this->last_time      = microtime(true);
 432  
 433          switch ($type) {
 434              case SQL_QUERY_SELECT:
 435              case SQL_QUERY_AUX:
 436                  $this->reads++;
 437                  break;
 438              case SQL_QUERY_INSERT:
 439              case SQL_QUERY_UPDATE:
 440              case SQL_QUERY_STRUCTURE:
 441                  $this->writes++;
 442              default:
 443                  if ((PHPUNIT_TEST) || (defined('BEHAT_TEST') && BEHAT_TEST) ||
 444                      defined('BEHAT_SITE_RUNNING')) {
 445  
 446                      // Set list of tables that are updated.
 447                      require_once (__DIR__.'/../testing/classes/util.php');
 448                      testing_util::set_table_modified_by_sql($sql);
 449                  }
 450          }
 451  
 452          $this->print_debug($sql, $params);
 453      }
 454  
 455      /**
 456       * This should be called immediately after each db query. It does a clean up of resources.
 457       * It also throws exceptions if the sql that ran produced errors.
 458       * @param mixed $result The db specific result obtained from running a query.
 459       * @throws dml_read_exception | dml_write_exception | ddl_change_structure_exception
 460       * @return void
 461       */
 462      protected function query_end($result) {
 463          if ($this->loggingquery) {
 464              return;
 465          }
 466          if ($result !== false) {
 467              $this->query_log();
 468              // free memory
 469              $this->last_sql    = null;
 470              $this->last_params = null;
 471              $this->print_debug_time();
 472              return;
 473          }
 474  
 475          // remember current info, log queries may alter it
 476          $type   = $this->last_type;
 477          $sql    = $this->last_sql;
 478          $params = $this->last_params;
 479          $error  = $this->get_last_error();
 480  
 481          $this->query_log($error);
 482  
 483          switch ($type) {
 484              case SQL_QUERY_SELECT:
 485              case SQL_QUERY_AUX:
 486                  throw new dml_read_exception($error, $sql, $params);
 487              case SQL_QUERY_INSERT:
 488              case SQL_QUERY_UPDATE:
 489                  throw new dml_write_exception($error, $sql, $params);
 490              case SQL_QUERY_STRUCTURE:
 491                  $this->get_manager(); // includes ddl exceptions classes ;-)
 492                  throw new ddl_change_structure_exception($error, $sql);
 493          }
 494      }
 495  
 496      /**
 497       * This logs the last query based on 'logall', 'logslow' and 'logerrors' options configured via $CFG->dboptions .
 498       * @param string|bool $error or false if not error
 499       * @return void
 500       */
 501      public function query_log($error=false) {
 502          // Logging disabled by the driver.
 503          if ($this->skiplogging) {
 504              return;
 505          }
 506  
 507          $logall    = !empty($this->dboptions['logall']);
 508          $logslow   = !empty($this->dboptions['logslow']) ? $this->dboptions['logslow'] : false;
 509          $logerrors = !empty($this->dboptions['logerrors']);
 510          $iserror   = ($error !== false);
 511  
 512          $time = $this->query_time();
 513  
 514          // Will be shown or not depending on MDL_PERF values rather than in dboptions['log*].
 515          $this->queriestime = $this->queriestime + $time;
 516  
 517          if ($logall or ($logslow and ($logslow < ($time+0.00001))) or ($iserror and $logerrors)) {
 518              $this->loggingquery = true;
 519              try {
 520                  $backtrace = debug_backtrace();
 521                  if ($backtrace) {
 522                      //remove query_log()
 523                      array_shift($backtrace);
 524                  }
 525                  if ($backtrace) {
 526                      //remove query_end()
 527                      array_shift($backtrace);
 528                  }
 529                  $log = new stdClass();
 530                  $log->qtype      = $this->last_type;
 531                  $log->sqltext    = $this->last_sql;
 532                  $log->sqlparams  = var_export((array)$this->last_params, true);
 533                  $log->error      = (int)$iserror;
 534                  $log->info       = $iserror ? $error : null;
 535                  $log->backtrace  = format_backtrace($backtrace, true);
 536                  $log->exectime   = $time;
 537                  $log->timelogged = time();
 538                  $this->insert_record('log_queries', $log);
 539              } catch (Exception $ignored) {
 540              }
 541              $this->loggingquery = false;
 542          }
 543      }
 544  
 545      /**
 546       * Disable logging temporarily.
 547       */
 548      protected function query_log_prevent() {
 549          $this->skiplogging = true;
 550      }
 551  
 552      /**
 553       * Restore old logging behavior.
 554       */
 555      protected function query_log_allow() {
 556          $this->skiplogging = false;
 557      }
 558  
 559      /**
 560       * Returns the time elapsed since the query started.
 561       * @return float Seconds with microseconds
 562       */
 563      protected function query_time() {
 564          return microtime(true) - $this->last_time;
 565      }
 566  
 567      /**
 568       * Returns database server info array
 569       * @return array Array containing 'description' and 'version' at least.
 570       */
 571      public abstract function get_server_info();
 572  
 573      /**
 574       * Returns supported query parameter types
 575       * @return int bitmask of accepted SQL_PARAMS_*
 576       */
 577      protected abstract function allowed_param_types();
 578  
 579      /**
 580       * Returns the last error reported by the database engine.
 581       * @return string The error message.
 582       */
 583      public abstract function get_last_error();
 584  
 585      /**
 586       * Prints sql debug info
 587       * @param string $sql The query which is being debugged.
 588       * @param array $params The query parameters. (optional)
 589       * @param mixed $obj The library specific object. (optional)
 590       * @return void
 591       */
 592      protected function print_debug($sql, array $params=null, $obj=null) {
 593          if (!$this->get_debug()) {
 594              return;
 595          }
 596          if (CLI_SCRIPT) {
 597              $separator = "--------------------------------\n";
 598              echo $separator;
 599              echo "{$sql}\n";
 600              if (!is_null($params)) {
 601                  echo "[" . var_export($params, true) . "]\n";
 602              }
 603              echo $separator;
 604          } else if (AJAX_SCRIPT) {
 605              $separator = "--------------------------------";
 606              error_log($separator);
 607              error_log($sql);
 608              if (!is_null($params)) {
 609                  error_log("[" . var_export($params, true) . "]");
 610              }
 611              error_log($separator);
 612          } else {
 613              $separator = "<hr />\n";
 614              echo $separator;
 615              echo s($sql) . "\n";
 616              if (!is_null($params)) {
 617                  echo "[" . s(var_export($params, true)) . "]\n";
 618              }
 619              echo $separator;
 620          }
 621      }
 622  
 623      /**
 624       * Prints the time a query took to run.
 625       * @return void
 626       */
 627      protected function print_debug_time() {
 628          if (!$this->get_debug()) {
 629              return;
 630          }
 631          $time = $this->query_time();
 632          $message = "Query took: {$time} seconds.\n";
 633          if (CLI_SCRIPT) {
 634              echo $message;
 635              echo "--------------------------------\n";
 636          } else if (AJAX_SCRIPT) {
 637              error_log($message);
 638              error_log("--------------------------------");
 639          } else {
 640              echo s($message);
 641              echo "<hr />\n";
 642          }
 643      }
 644  
 645      /**
 646       * Returns the SQL WHERE conditions.
 647       * @param string $table The table name that these conditions will be validated against.
 648       * @param array $conditions The conditions to build the where clause. (must not contain numeric indexes)
 649       * @throws dml_exception
 650       * @return array An array list containing sql 'where' part and 'params'.
 651       */
 652      protected function where_clause($table, array $conditions=null) {
 653          // We accept nulls in conditions
 654          $conditions = is_null($conditions) ? array() : $conditions;
 655  
 656          if (empty($conditions)) {
 657              return array('', array());
 658          }
 659  
 660          // Some checks performed under debugging only
 661          if (debugging()) {
 662              $columns = $this->get_columns($table);
 663              if (empty($columns)) {
 664                  // no supported columns means most probably table does not exist
 665                  throw new dml_exception('ddltablenotexist', $table);
 666              }
 667              foreach ($conditions as $key=>$value) {
 668                  if (!isset($columns[$key])) {
 669                      $a = new stdClass();
 670                      $a->fieldname = $key;
 671                      $a->tablename = $table;
 672                      throw new dml_exception('ddlfieldnotexist', $a);
 673                  }
 674                  $column = $columns[$key];
 675                  if ($column->meta_type == 'X') {
 676                      //ok so the column is a text column. sorry no text columns in the where clause conditions
 677                      throw new dml_exception('textconditionsnotallowed', $conditions);
 678                  }
 679              }
 680          }
 681  
 682          $allowed_types = $this->allowed_param_types();
 683          $where = array();
 684          $params = array();
 685  
 686          foreach ($conditions as $key=>$value) {
 687              if (is_int($key)) {
 688                  throw new dml_exception('invalidnumkey');
 689              }
 690              if (is_null($value)) {
 691                  $where[] = "$key IS NULL";
 692              } else {
 693                  if ($allowed_types & SQL_PARAMS_NAMED) {
 694                      // Need to verify key names because they can contain, originally,
 695                      // spaces and other forbidden chars when using sql_xxx() functions and friends.
 696                      $normkey = trim(preg_replace('/[^a-zA-Z0-9_-]/', '_', $key), '-_');
 697                      if ($normkey !== $key) {
 698                          debugging('Invalid key found in the conditions array.');
 699                      }
 700                      $where[] = "$key = :$normkey";
 701                      $params[$normkey] = $value;
 702                  } else {
 703                      $where[] = "$key = ?";
 704                      $params[] = $value;
 705                  }
 706              }
 707          }
 708          $where = implode(" AND ", $where);
 709          return array($where, $params);
 710      }
 711  
 712      /**
 713       * Returns SQL WHERE conditions for the ..._list group of methods.
 714       *
 715       * @param string $field the name of a field.
 716       * @param array $values the values field might take.
 717       * @return array An array containing sql 'where' part and 'params'
 718       */
 719      protected function where_clause_list($field, array $values) {
 720          if (empty($values)) {
 721              return array("1 = 2", array()); // Fake condition, won't return rows ever. MDL-17645
 722          }
 723  
 724          // Note: Do not use get_in_or_equal() because it can not deal with bools and nulls.
 725  
 726          $params = array();
 727          $select = "";
 728          $values = (array)$values;
 729          foreach ($values as $value) {
 730              if (is_bool($value)) {
 731                  $value = (int)$value;
 732              }
 733              if (is_null($value)) {
 734                  $select = "$field IS NULL";
 735              } else {
 736                  $params[] = $value;
 737              }
 738          }
 739          if ($params) {
 740              if ($select !== "") {
 741                  $select = "$select OR ";
 742              }
 743              $count = count($params);
 744              if ($count == 1) {
 745                  $select = $select."$field = ?";
 746              } else {
 747                  $qs = str_repeat(',?', $count);
 748                  $qs = ltrim($qs, ',');
 749                  $select = $select."$field IN ($qs)";
 750              }
 751          }
 752          return array($select, $params);
 753      }
 754  
 755      /**
 756       * Constructs 'IN()' or '=' sql fragment
 757       * @param mixed $items A single value or array of values for the expression.
 758       * @param int $type Parameter bounding type : SQL_PARAMS_QM or SQL_PARAMS_NAMED.
 759       * @param string $prefix Named parameter placeholder prefix (a unique counter value is appended to each parameter name).
 760       * @param bool $equal True means we want to equate to the constructed expression, false means we don't want to equate to it.
 761       * @param mixed $onemptyitems This defines the behavior when the array of items provided is empty. Defaults to false,
 762       *              meaning throw exceptions. Other values will become part of the returned SQL fragment.
 763       * @throws coding_exception | dml_exception
 764       * @return array A list containing the constructed sql fragment and an array of parameters.
 765       */
 766      public function get_in_or_equal($items, $type=SQL_PARAMS_QM, $prefix='param', $equal=true, $onemptyitems=false) {
 767  
 768          // default behavior, throw exception on empty array
 769          if (is_array($items) and empty($items) and $onemptyitems === false) {
 770              throw new coding_exception('moodle_database::get_in_or_equal() does not accept empty arrays');
 771          }
 772          // handle $onemptyitems on empty array of items
 773          if (is_array($items) and empty($items)) {
 774              if (is_null($onemptyitems)) {             // Special case, NULL value
 775                  $sql = $equal ? ' IS NULL' : ' IS NOT NULL';
 776                  return (array($sql, array()));
 777              } else {
 778                  $items = array($onemptyitems);        // Rest of cases, prepare $items for std processing
 779              }
 780          }
 781  
 782          if ($type == SQL_PARAMS_QM) {
 783              if (!is_array($items) or count($items) == 1) {
 784                  $sql = $equal ? '= ?' : '<> ?';
 785                  $items = (array)$items;
 786                  $params = array_values($items);
 787              } else {
 788                  if ($equal) {
 789                      $sql = 'IN ('.implode(',', array_fill(0, count($items), '?')).')';
 790                  } else {
 791                      $sql = 'NOT IN ('.implode(',', array_fill(0, count($items), '?')).')';
 792                  }
 793                  $params = array_values($items);
 794              }
 795  
 796          } else if ($type == SQL_PARAMS_NAMED) {
 797              if (empty($prefix)) {
 798                  $prefix = 'param';
 799              }
 800  
 801              if (!is_array($items)){
 802                  $param = $prefix.$this->inorequaluniqueindex++;
 803                  $sql = $equal ? "= :$param" : "<> :$param";
 804                  $params = array($param=>$items);
 805              } else if (count($items) == 1) {
 806                  $param = $prefix.$this->inorequaluniqueindex++;
 807                  $sql = $equal ? "= :$param" : "<> :$param";
 808                  $item = reset($items);
 809                  $params = array($param=>$item);
 810              } else {
 811                  $params = array();
 812                  $sql = array();
 813                  foreach ($items as $item) {
 814                      $param = $prefix.$this->inorequaluniqueindex++;
 815                      $params[$param] = $item;
 816                      $sql[] = ':'.$param;
 817                  }
 818                  if ($equal) {
 819                      $sql = 'IN ('.implode(',', $sql).')';
 820                  } else {
 821                      $sql = 'NOT IN ('.implode(',', $sql).')';
 822                  }
 823              }
 824  
 825          } else {
 826              throw new dml_exception('typenotimplement');
 827          }
 828          return array($sql, $params);
 829      }
 830  
 831      /**
 832       * Converts short table name {tablename} to the real prefixed table name in given sql.
 833       * @param string $sql The sql to be operated on.
 834       * @return string The sql with tablenames being prefixed with $CFG->prefix
 835       */
 836      protected function fix_table_names($sql) {
 837          return preg_replace_callback(
 838              '/\{([a-z][a-z0-9_]*)\}/',
 839              function($matches) {
 840                  return $this->fix_table_name($matches[1]);
 841              },
 842              $sql
 843          );
 844      }
 845  
 846      /**
 847       * Adds the prefix to the table name.
 848       *
 849       * @param string $tablename The table name
 850       * @return string The prefixed table name
 851       */
 852      protected function fix_table_name($tablename) {
 853          return $this->prefix . $tablename;
 854      }
 855  
 856      /**
 857       * Internal private utitlity function used to fix parameters.
 858       * Used with {@link preg_replace_callback()}
 859       * @param array $match Refer to preg_replace_callback usage for description.
 860       * @return string
 861       */
 862      private function _fix_sql_params_dollar_callback($match) {
 863          $this->fix_sql_params_i++;
 864          return "\$".$this->fix_sql_params_i;
 865      }
 866  
 867      /**
 868       * Detects object parameters and throws exception if found
 869       * @param mixed $value
 870       * @return void
 871       * @throws coding_exception if object detected
 872       */
 873      protected function detect_objects($value) {
 874          if (is_object($value)) {
 875              throw new coding_exception('Invalid database query parameter value', 'Objects are are not allowed: '.get_class($value));
 876          }
 877      }
 878  
 879      /**
 880       * Normalizes sql query parameters and verifies parameters.
 881       * @param string $sql The query or part of it.
 882       * @param array $params The query parameters.
 883       * @return array (sql, params, type of params)
 884       */
 885      public function fix_sql_params($sql, array $params=null) {
 886          $params = (array)$params; // mke null array if needed
 887          $allowed_types = $this->allowed_param_types();
 888  
 889          // convert table names
 890          $sql = $this->fix_table_names($sql);
 891  
 892          // cast booleans to 1/0 int and detect forbidden objects
 893          foreach ($params as $key => $value) {
 894              $this->detect_objects($value);
 895              $params[$key] = is_bool($value) ? (int)$value : $value;
 896          }
 897  
 898          // NICOLAS C: Fixed regexp for negative backwards look-ahead of double colons. Thanks for Sam Marshall's help
 899          $named_count = preg_match_all('/(?<!:):[a-z][a-z0-9_]*/', $sql, $named_matches); // :: used in pgsql casts
 900          $dollar_count = preg_match_all('/\$[1-9][0-9]*/', $sql, $dollar_matches);
 901          $q_count     = substr_count($sql, '?');
 902  
 903          // Optionally add debug trace to sql as a comment.
 904          $sql = $this->add_sql_debugging($sql);
 905  
 906          $count = 0;
 907  
 908          if ($named_count) {
 909              $type = SQL_PARAMS_NAMED;
 910              $count = $named_count;
 911  
 912          }
 913          if ($dollar_count) {
 914              if ($count) {
 915                  throw new dml_exception('mixedtypesqlparam');
 916              }
 917              $type = SQL_PARAMS_DOLLAR;
 918              $count = $dollar_count;
 919  
 920          }
 921          if ($q_count) {
 922              if ($count) {
 923                  throw new dml_exception('mixedtypesqlparam');
 924              }
 925              $type = SQL_PARAMS_QM;
 926              $count = $q_count;
 927  
 928          }
 929  
 930          if (!$count) {
 931               // ignore params
 932              if ($allowed_types & SQL_PARAMS_NAMED) {
 933                  return array($sql, array(), SQL_PARAMS_NAMED);
 934              } else if ($allowed_types & SQL_PARAMS_QM) {
 935                  return array($sql, array(), SQL_PARAMS_QM);
 936              } else {
 937                  return array($sql, array(), SQL_PARAMS_DOLLAR);
 938              }
 939          }
 940  
 941          if ($count > count($params)) {
 942              $a = new stdClass;
 943              $a->expected = $count;
 944              $a->actual = count($params);
 945              throw new dml_exception('invalidqueryparam', $a);
 946          }
 947  
 948          $target_type = $allowed_types;
 949  
 950          if ($type & $allowed_types) { // bitwise AND
 951              if ($count == count($params)) {
 952                  if ($type == SQL_PARAMS_QM) {
 953                      return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based array required
 954                  } else {
 955                      //better do the validation of names below
 956                  }
 957              }
 958              // needs some fixing or validation - there might be more params than needed
 959              $target_type = $type;
 960          }
 961  
 962          if ($type == SQL_PARAMS_NAMED) {
 963              $finalparams = array();
 964              foreach ($named_matches[0] as $key) {
 965                  $key = trim($key, ':');
 966                  if (!array_key_exists($key, $params)) {
 967                      throw new dml_exception('missingkeyinsql', $key, '');
 968                  }
 969                  if (strlen($key) > 30) {
 970                      throw new coding_exception(
 971                              "Placeholder names must be 30 characters or shorter. '" .
 972                              $key . "' is too long.", $sql);
 973                  }
 974                  $finalparams[$key] = $params[$key];
 975              }
 976              if ($count != count($finalparams)) {
 977                  throw new dml_exception('duplicateparaminsql');
 978              }
 979  
 980              if ($target_type & SQL_PARAMS_QM) {
 981                  $sql = preg_replace('/(?<!:):[a-z][a-z0-9_]*/', '?', $sql);
 982                  return array($sql, array_values($finalparams), SQL_PARAMS_QM); // 0-based required
 983              } else if ($target_type & SQL_PARAMS_NAMED) {
 984                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
 985              } else {  // $type & SQL_PARAMS_DOLLAR
 986                  //lambda-style functions eat memory - we use globals instead :-(
 987                  $this->fix_sql_params_i = 0;
 988                  $sql = preg_replace_callback('/(?<!:):[a-z][a-z0-9_]*/', array($this, '_fix_sql_params_dollar_callback'), $sql);
 989                  return array($sql, array_values($finalparams), SQL_PARAMS_DOLLAR); // 0-based required
 990              }
 991  
 992          } else if ($type == SQL_PARAMS_DOLLAR) {
 993              if ($target_type & SQL_PARAMS_DOLLAR) {
 994                  return array($sql, array_values($params), SQL_PARAMS_DOLLAR); // 0-based required
 995              } else if ($target_type & SQL_PARAMS_QM) {
 996                  $sql = preg_replace('/\$[0-9]+/', '?', $sql);
 997                  return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based required
 998              } else { //$target_type & SQL_PARAMS_NAMED
 999                  $sql = preg_replace('/\$([0-9]+)/', ':param\\1', $sql);
1000                  $finalparams = array();
1001                  foreach ($params as $key=>$param) {
1002                      $key++;
1003                      $finalparams['param'.$key] = $param;
1004                  }
1005                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
1006              }
1007  
1008          } else { // $type == SQL_PARAMS_QM
1009              if (count($params) != $count) {
1010                  $params = array_slice($params, 0, $count);
1011              }
1012  
1013              if ($target_type & SQL_PARAMS_QM) {
1014                  return array($sql, array_values($params), SQL_PARAMS_QM); // 0-based required
1015              } else if ($target_type & SQL_PARAMS_NAMED) {
1016                  $finalparams = array();
1017                  $pname = 'param0';
1018                  $parts = explode('?', $sql);
1019                  $sql = array_shift($parts);
1020                  foreach ($parts as $part) {
1021                      $param = array_shift($params);
1022                      $pname++;
1023                      $sql .= ':'.$pname.$part;
1024                      $finalparams[$pname] = $param;
1025                  }
1026                  return array($sql, $finalparams, SQL_PARAMS_NAMED);
1027              } else {  // $type & SQL_PARAMS_DOLLAR
1028                  //lambda-style functions eat memory - we use globals instead :-(
1029                  $this->fix_sql_params_i = 0;
1030                  $sql = preg_replace_callback('/\?/', array($this, '_fix_sql_params_dollar_callback'), $sql);
1031                  return array($sql, array_values($params), SQL_PARAMS_DOLLAR); // 0-based required
1032              }
1033          }
1034      }
1035  
1036      /**
1037       * Add an SQL comment to trace all sql calls back to the calling php code
1038       * @param string $sql Original sql
1039       * @return string Instrumented sql
1040       */
1041      protected function add_sql_debugging(string $sql): string {
1042          global $CFG;
1043  
1044          if (!property_exists($CFG, 'debugsqltrace')) {
1045              return $sql;
1046          }
1047  
1048          $level = $CFG->debugsqltrace;
1049  
1050          if (empty($level)) {
1051              return $sql;
1052          }
1053  
1054          $callers = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
1055  
1056          // Ignore moodle_database internals.
1057          $callers = array_filter($callers, function($caller) {
1058              return empty($caller['class']) || $caller['class'] != 'moodle_database';
1059          });
1060  
1061          $callers = array_slice($callers, 0, $level);
1062  
1063          $text = trim(format_backtrace($callers, true));
1064  
1065          // Convert all linebreaks to SQL comments, optionally
1066          // also eating any * formatting.
1067          $text = preg_replace("/(^|\n)\*?\s*/", "\n-- ", $text);
1068  
1069          // Convert all ? to 'unknown' in the sql coment so these don't get
1070          // caught by fix_sql_params().
1071          $text = str_replace('?', 'unknown', $text);
1072  
1073          // Convert tokens like :test to ::test for the same reason.
1074          $text = preg_replace('/(?<!:):[a-z][a-z0-9_]*/', ':\0', $text);
1075  
1076          return $sql . $text;
1077      }
1078  
1079  
1080      /**
1081       * Ensures that limit params are numeric and positive integers, to be passed to the database.
1082       * We explicitly treat null, '' and -1 as 0 in order to provide compatibility with how limit
1083       * values have been passed historically.
1084       *
1085       * @param int $limitfrom Where to start results from
1086       * @param int $limitnum How many results to return
1087       * @return array Normalised limit params in array($limitfrom, $limitnum)
1088       */
1089      protected function normalise_limit_from_num($limitfrom, $limitnum) {
1090          global $CFG;
1091  
1092          // We explicilty treat these cases as 0.
1093          if ($limitfrom === null || $limitfrom === '' || $limitfrom === -1) {
1094              $limitfrom = 0;
1095          }
1096          if ($limitnum === null || $limitnum === '' || $limitnum === -1) {
1097              $limitnum = 0;
1098          }
1099  
1100          if ($CFG->debugdeveloper) {
1101              if (!is_numeric($limitfrom)) {
1102                  $strvalue = var_export($limitfrom, true);
1103                  debugging("Non-numeric limitfrom parameter detected: $strvalue, did you pass the correct arguments?",
1104                      DEBUG_DEVELOPER);
1105              } else if ($limitfrom < 0) {
1106                  debugging("Negative limitfrom parameter detected: $limitfrom, did you pass the correct arguments?",
1107                      DEBUG_DEVELOPER);
1108              }
1109  
1110              if (!is_numeric($limitnum)) {
1111                  $strvalue = var_export($limitnum, true);
1112                  debugging("Non-numeric limitnum parameter detected: $strvalue, did you pass the correct arguments?",
1113                      DEBUG_DEVELOPER);
1114              } else if ($limitnum < 0) {
1115                  debugging("Negative limitnum parameter detected: $limitnum, did you pass the correct arguments?",
1116                      DEBUG_DEVELOPER);
1117              }
1118          }
1119  
1120          $limitfrom = (int)$limitfrom;
1121          $limitnum  = (int)$limitnum;
1122          $limitfrom = max(0, $limitfrom);
1123          $limitnum  = max(0, $limitnum);
1124  
1125          return array($limitfrom, $limitnum);
1126      }
1127  
1128      /**
1129       * Return tables in database WITHOUT current prefix.
1130       * @param bool $usecache if true, returns list of cached tables.
1131       * @return array of table names in lowercase and without prefix
1132       */
1133      public abstract function get_tables($usecache=true);
1134  
1135      /**
1136       * Return table indexes - everything lowercased.
1137       * @param string $table The table we want to get indexes from.
1138       * @return array An associative array of indexes containing 'unique' flag and 'columns' being indexed
1139       */
1140      public abstract function get_indexes($table);
1141  
1142      /**
1143       * Returns detailed information about columns in table. This information is cached internally.
1144       *
1145       * @param string $table The table's name.
1146       * @param bool $usecache Flag to use internal cacheing. The default is true.
1147       * @return database_column_info[] of database_column_info objects indexed with column names
1148       */
1149      public function get_columns($table, $usecache = true): array {
1150          if (!$table) { // Table not specified, return empty array directly.
1151              return [];
1152          }
1153  
1154          if ($usecache) {
1155              if ($this->temptables->is_temptable($table)) {
1156                  if ($data = $this->get_temp_tables_cache()->get($table)) {
1157                      return $data;
1158                  }
1159              } else {
1160                  if ($data = $this->get_metacache()->get($table)) {
1161                      return $data;
1162                  }
1163              }
1164          }
1165  
1166          $structure = $this->fetch_columns($table);
1167  
1168          if ($usecache) {
1169              if ($this->temptables->is_temptable($table)) {
1170                  $this->get_temp_tables_cache()->set($table, $structure);
1171              } else {
1172                  $this->get_metacache()->set($table, $structure);
1173              }
1174          }
1175  
1176          return $structure;
1177      }
1178  
1179      /**
1180       * Returns detailed information about columns in table. This information is cached internally.
1181       *
1182       * @param string $table The table's name.
1183       * @return database_column_info[] of database_column_info objects indexed with column names
1184       */
1185      protected abstract function fetch_columns(string $table): array;
1186  
1187      /**
1188       * Normalise values based on varying RDBMS's dependencies (booleans, LOBs...)
1189       *
1190       * @param database_column_info $column column metadata corresponding with the value we are going to normalise
1191       * @param mixed $value value we are going to normalise
1192       * @return mixed the normalised value
1193       */
1194      protected abstract function normalise_value($column, $value);
1195  
1196      /**
1197       * Resets the internal column details cache
1198       *
1199       * @param array|null $tablenames an array of xmldb table names affected by this request.
1200       * @return void
1201       */
1202      public function reset_caches($tablenames = null) {
1203          if (!empty($tablenames)) {
1204              $dbmetapurged = false;
1205              foreach ($tablenames as $tablename) {
1206                  if ($this->temptables->is_temptable($tablename)) {
1207                      $this->get_temp_tables_cache()->delete($tablename);
1208                  } else if ($dbmetapurged === false) {
1209                      $this->tables = null;
1210                      $this->get_metacache()->purge();
1211                      $this->metacache = null;
1212                      $dbmetapurged = true;
1213                  }
1214              }
1215          } else {
1216              $this->get_temp_tables_cache()->purge();
1217              $this->tables = null;
1218              // Purge MUC as well.
1219              $this->get_metacache()->purge();
1220              $this->metacache = null;
1221          }
1222      }
1223  
1224      /**
1225       * Returns the sql generator used for db manipulation.
1226       * Used mostly in upgrade.php scripts.
1227       * @return database_manager The instance used to perform ddl operations.
1228       * @see lib/ddl/database_manager.php
1229       */
1230      public function get_manager() {
1231          global $CFG;
1232  
1233          if (!$this->database_manager) {
1234              require_once($CFG->libdir.'/ddllib.php');
1235  
1236              $classname = $this->get_dbfamily().'_sql_generator';
1237              require_once("$CFG->libdir/ddl/$classname.php");
1238              $generator = new $classname($this, $this->temptables);
1239  
1240              $this->database_manager = new database_manager($this, $generator);
1241          }
1242          return $this->database_manager;
1243      }
1244  
1245      /**
1246       * Attempts to change db encoding to UTF-8 encoding if possible.
1247       * @return bool True is successful.
1248       */
1249      public function change_db_encoding() {
1250          return false;
1251      }
1252  
1253      /**
1254       * Checks to see if the database is in unicode mode?
1255       * @return bool
1256       */
1257      public function setup_is_unicodedb() {
1258          return true;
1259      }
1260  
1261      /**
1262       * Enable/disable very detailed debugging.
1263       * @param bool $state
1264       * @return void
1265       */
1266      public function set_debug($state) {
1267          $this->debug = $state;
1268      }
1269  
1270      /**
1271       * Returns debug status
1272       * @return bool $state
1273       */
1274      public function get_debug() {
1275          return $this->debug;
1276      }
1277  
1278      /**
1279       * Enable/disable detailed sql logging
1280       *
1281       * @deprecated since Moodle 2.9
1282       */
1283      public function set_logging($state) {
1284          throw new coding_exception('set_logging() can not be used any more.');
1285      }
1286  
1287      /**
1288       * Do NOT use in code, this is for use by database_manager only!
1289       * @param string|array $sql query or array of queries
1290       * @param array|null $tablenames an array of xmldb table names affected by this request.
1291       * @return bool true
1292       * @throws ddl_change_structure_exception A DDL specific exception is thrown for any errors.
1293       */
1294      public abstract function change_database_structure($sql, $tablenames = null);
1295  
1296      /**
1297       * Executes a general sql query. Should be used only when no other method suitable.
1298       * Do NOT use this to make changes in db structure, use database_manager methods instead!
1299       * @param string $sql query
1300       * @param array $params query parameters
1301       * @return bool true
1302       * @throws dml_exception A DML specific exception is thrown for any errors.
1303       */
1304      public abstract function execute($sql, array $params=null);
1305  
1306      /**
1307       * Get a number of records as a moodle_recordset where all the given conditions met.
1308       *
1309       * Selects records from the table $table.
1310       *
1311       * If specified, only records meeting $conditions.
1312       *
1313       * If specified, the results will be sorted as specified by $sort. This
1314       * is added to the SQL as "ORDER BY $sort". Example values of $sort
1315       * might be "time ASC" or "time DESC".
1316       *
1317       * If $fields is specified, only those fields are returned.
1318       *
1319       * Since this method is a little less readable, use of it should be restricted to
1320       * code where it's possible there might be large datasets being returned.  For known
1321       * small datasets use get_records - it leads to simpler code.
1322       *
1323       * If you only want some of the records, specify $limitfrom and $limitnum.
1324       * The query will skip the first $limitfrom records (according to the sort
1325       * order) and then return the next $limitnum records. If either of $limitfrom
1326       * or $limitnum is specified, both must be present.
1327       *
1328       * The return value is a moodle_recordset
1329       * if the query succeeds. If an error occurs, false is returned.
1330       *
1331       * @param string $table the table to query.
1332       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1333       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1334       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1335       * @param int $limitfrom return a subset of records, starting at this point (optional).
1336       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1337       * @return moodle_recordset A moodle_recordset instance
1338       * @throws dml_exception A DML specific exception is thrown for any errors.
1339       */
1340      public function get_recordset($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1341          list($select, $params) = $this->where_clause($table, $conditions);
1342          return $this->get_recordset_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1343      }
1344  
1345      /**
1346       * Get a number of records as a moodle_recordset where one field match one list of values.
1347       *
1348       * Only records where $field takes one of the values $values are returned.
1349       * $values must be an array of values.
1350       *
1351       * Other arguments and the return type are like {@link function get_recordset}.
1352       *
1353       * @param string $table the table to query.
1354       * @param string $field a field to check (optional).
1355       * @param array $values array of values the field must have
1356       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1357       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1358       * @param int $limitfrom return a subset of records, starting at this point (optional).
1359       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1360       * @return moodle_recordset A moodle_recordset instance.
1361       * @throws dml_exception A DML specific exception is thrown for any errors.
1362       */
1363      public function get_recordset_list($table, $field, array $values, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1364          list($select, $params) = $this->where_clause_list($field, $values);
1365          return $this->get_recordset_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1366      }
1367  
1368      /**
1369       * Get a number of records as a moodle_recordset which match a particular WHERE clause.
1370       *
1371       * If given, $select is used as the SELECT parameter in the SQL query,
1372       * otherwise all records from the table are returned.
1373       *
1374       * Other arguments and the return type are like {@link function get_recordset}.
1375       *
1376       * @param string $table the table to query.
1377       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1378       * @param array $params array of sql parameters
1379       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1380       * @param string $fields a comma separated list of fields to return (optional, by default all fields are returned).
1381       * @param int $limitfrom return a subset of records, starting at this point (optional).
1382       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1383       * @return moodle_recordset A moodle_recordset instance.
1384       * @throws dml_exception A DML specific exception is thrown for any errors.
1385       */
1386      public function get_recordset_select($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1387          $sql = "SELECT $fields FROM {".$table."}";
1388          if ($select) {
1389              $sql .= " WHERE $select";
1390          }
1391          if ($sort) {
1392              $sql .= " ORDER BY $sort";
1393          }
1394          return $this->get_recordset_sql($sql, $params, $limitfrom, $limitnum);
1395      }
1396  
1397      /**
1398       * Get a number of records as a moodle_recordset using a SQL statement.
1399       *
1400       * Since this method is a little less readable, use of it should be restricted to
1401       * code where it's possible there might be large datasets being returned.  For known
1402       * small datasets use get_records_sql - it leads to simpler code.
1403       *
1404       * The return type is like {@link function get_recordset}.
1405       *
1406       * @param string $sql the SQL select query to execute.
1407       * @param array $params array of sql parameters
1408       * @param int $limitfrom return a subset of records, starting at this point (optional).
1409       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1410       * @return moodle_recordset A moodle_recordset instance.
1411       * @throws dml_exception A DML specific exception is thrown for any errors.
1412       */
1413      public abstract function get_recordset_sql($sql, array $params=null, $limitfrom=0, $limitnum=0);
1414  
1415      /**
1416       * Get all records from a table.
1417       *
1418       * This method works around potential memory problems and may improve performance,
1419       * this method may block access to table until the recordset is closed.
1420       *
1421       * @param string $table Name of database table.
1422       * @return moodle_recordset A moodle_recordset instance {@link function get_recordset}.
1423       * @throws dml_exception A DML specific exception is thrown for any errors.
1424       */
1425      public function export_table_recordset($table) {
1426          return $this->get_recordset($table, array());
1427      }
1428  
1429      /**
1430       * Get a number of records as an array of objects where all the given conditions met.
1431       *
1432       * If the query succeeds and returns at least one record, the
1433       * return value is an array of objects, one object for each
1434       * record found. The array key is the value from the first
1435       * column of the result set. The object associated with that key
1436       * has a member variable for each column of the results.
1437       *
1438       * @param string $table the table to query.
1439       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1440       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1441       * @param string $fields a comma separated list of fields to return (optional, by default
1442       *   all fields are returned). The first field will be used as key for the
1443       *   array so must be a unique field such as 'id'.
1444       * @param int $limitfrom return a subset of records, starting at this point (optional).
1445       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1446       * @return array An array of Objects indexed by first column.
1447       * @throws dml_exception A DML specific exception is thrown for any errors.
1448       */
1449      public function get_records($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1450          list($select, $params) = $this->where_clause($table, $conditions);
1451          return $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1452      }
1453  
1454      /**
1455       * Get a number of records as an array of objects where one field match one list of values.
1456       *
1457       * Return value is like {@link function get_records}.
1458       *
1459       * @param string $table The database table to be checked against.
1460       * @param string $field The field to search
1461       * @param array $values An array of values
1462       * @param string $sort Sort order (as valid SQL sort parameter)
1463       * @param string $fields A comma separated list of fields to be returned from the chosen table. If specified,
1464       *   the first field should be a unique one such as 'id' since it will be used as a key in the associative
1465       *   array.
1466       * @param int $limitfrom return a subset of records, starting at this point (optional).
1467       * @param int $limitnum return a subset comprising this many records in total (optional).
1468       * @return array An array of objects indexed by first column
1469       * @throws dml_exception A DML specific exception is thrown for any errors.
1470       */
1471      public function get_records_list($table, $field, array $values, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1472          list($select, $params) = $this->where_clause_list($field, $values);
1473          return $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum);
1474      }
1475  
1476      /**
1477       * Get a number of records as an array of objects which match a particular WHERE clause.
1478       *
1479       * Return value is like {@link function get_records}.
1480       *
1481       * @param string $table The table to query.
1482       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1483       * @param array $params An array of sql parameters
1484       * @param string $sort An order to sort the results in (optional, a valid SQL ORDER BY parameter).
1485       * @param string $fields A comma separated list of fields to return
1486       *   (optional, by default all fields are returned). The first field will be used as key for the
1487       *   array so must be a unique field such as 'id'.
1488       * @param int $limitfrom return a subset of records, starting at this point (optional).
1489       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1490       * @return array of objects indexed by first column
1491       * @throws dml_exception A DML specific exception is thrown for any errors.
1492       */
1493      public function get_records_select($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1494          if ($select) {
1495              $select = "WHERE $select";
1496          }
1497          if ($sort) {
1498              $sort = " ORDER BY $sort";
1499          }
1500          return $this->get_records_sql("SELECT $fields FROM {" . $table . "} $select $sort", $params, $limitfrom, $limitnum);
1501      }
1502  
1503      /**
1504       * Get a number of records as an array of objects using a SQL statement.
1505       *
1506       * Return value is like {@link function get_records}.
1507       *
1508       * @param string $sql the SQL select query to execute. The first column of this SELECT statement
1509       *   must be a unique value (usually the 'id' field), as it will be used as the key of the
1510       *   returned array.
1511       * @param array $params array of sql parameters
1512       * @param int $limitfrom return a subset of records, starting at this point (optional).
1513       * @param int $limitnum return a subset comprising this many records in total (optional, required if $limitfrom is set).
1514       * @return array of objects indexed by first column
1515       * @throws dml_exception A DML specific exception is thrown for any errors.
1516       */
1517      public abstract function get_records_sql($sql, array $params=null, $limitfrom=0, $limitnum=0);
1518  
1519      /**
1520       * Get the first two columns from a number of records as an associative array where all the given conditions met.
1521       *
1522       * Arguments are like {@link function get_recordset}.
1523       *
1524       * If no errors occur the return value
1525       * is an associative whose keys come from the first field of each record,
1526       * and whose values are the corresponding second fields.
1527       * False is returned if an error occurs.
1528       *
1529       * @param string $table the table to query.
1530       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1531       * @param string $sort an order to sort the results in (optional, a valid SQL ORDER BY parameter).
1532       * @param string $fields a comma separated list of fields to return - the number of fields should be 2!
1533       * @param int $limitfrom return a subset of records, starting at this point (optional).
1534       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1535       * @return array an associative array
1536       * @throws dml_exception A DML specific exception is thrown for any errors.
1537       */
1538      public function get_records_menu($table, array $conditions=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1539          $menu = array();
1540          if ($records = $this->get_records($table, $conditions, $sort, $fields, $limitfrom, $limitnum)) {
1541              foreach ($records as $record) {
1542                  $record = (array)$record;
1543                  $key   = array_shift($record);
1544                  $value = array_shift($record);
1545                  $menu[$key] = $value;
1546              }
1547          }
1548          return $menu;
1549      }
1550  
1551      /**
1552       * Get the first two columns from a number of records as an associative array which match a particular WHERE clause.
1553       *
1554       * Arguments are like {@link function get_recordset_select}.
1555       * Return value is like {@link function get_records_menu}.
1556       *
1557       * @param string $table The database table to be checked against.
1558       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1559       * @param array $params array of sql parameters
1560       * @param string $sort Sort order (optional) - a valid SQL order parameter
1561       * @param string $fields A comma separated list of fields to be returned from the chosen table - the number of fields should be 2!
1562       * @param int $limitfrom return a subset of records, starting at this point (optional).
1563       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1564       * @return array an associative array
1565       * @throws dml_exception A DML specific exception is thrown for any errors.
1566       */
1567      public function get_records_select_menu($table, $select, array $params=null, $sort='', $fields='*', $limitfrom=0, $limitnum=0) {
1568          $menu = array();
1569          if ($records = $this->get_records_select($table, $select, $params, $sort, $fields, $limitfrom, $limitnum)) {
1570              foreach ($records as $record) {
1571                  $record = (array)$record;
1572                  $key   = array_shift($record);
1573                  $value = array_shift($record);
1574                  $menu[$key] = $value;
1575              }
1576          }
1577          return $menu;
1578      }
1579  
1580      /**
1581       * Get the first two columns from a number of records as an associative array using a SQL statement.
1582       *
1583       * Arguments are like {@link function get_recordset_sql}.
1584       * Return value is like {@link function get_records_menu}.
1585       *
1586       * @param string $sql The SQL string you wish to be executed.
1587       * @param array $params array of sql parameters
1588       * @param int $limitfrom return a subset of records, starting at this point (optional).
1589       * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
1590       * @return array an associative array
1591       * @throws dml_exception A DML specific exception is thrown for any errors.
1592       */
1593      public function get_records_sql_menu($sql, array $params=null, $limitfrom=0, $limitnum=0) {
1594          $menu = array();
1595          if ($records = $this->get_records_sql($sql, $params, $limitfrom, $limitnum)) {
1596              foreach ($records as $record) {
1597                  $record = (array)$record;
1598                  $key   = array_shift($record);
1599                  $value = array_shift($record);
1600                  $menu[$key] = $value;
1601              }
1602          }
1603          return $menu;
1604      }
1605  
1606      /**
1607       * Get a single database record as an object where all the given conditions met.
1608       *
1609       * @param string $table The table to select from.
1610       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1611       * @param string $fields A comma separated list of fields to be returned from the chosen table.
1612       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1613       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1614       *                        MUST_EXIST means we will throw an exception if no record or multiple records found.
1615       *
1616       * @todo MDL-30407 MUST_EXIST option should not throw a dml_exception, it should throw a different exception as it's a requested check.
1617       * @return mixed a fieldset object containing the first matching record, false or exception if error not found depending on mode
1618       * @throws dml_exception A DML specific exception is thrown for any errors.
1619       */
1620      public function get_record($table, array $conditions, $fields='*', $strictness=IGNORE_MISSING) {
1621          list($select, $params) = $this->where_clause($table, $conditions);
1622          return $this->get_record_select($table, $select, $params, $fields, $strictness);
1623      }
1624  
1625      /**
1626       * Get a single database record as an object which match a particular WHERE clause.
1627       *
1628       * @param string $table The database table to be checked against.
1629       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1630       * @param array $params array of sql parameters
1631       * @param string $fields A comma separated list of fields to be returned from the chosen table.
1632       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1633       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1634       *                        MUST_EXIST means throw exception if no record or multiple records found
1635       * @return stdClass|false a fieldset object containing the first matching record, false or exception if error not found depending on mode
1636       * @throws dml_exception A DML specific exception is thrown for any errors.
1637       */
1638      public function get_record_select($table, $select, array $params=null, $fields='*', $strictness=IGNORE_MISSING) {
1639          if ($select) {
1640              $select = "WHERE $select";
1641          }
1642          try {
1643              return $this->get_record_sql("SELECT $fields FROM {" . $table . "} $select", $params, $strictness);
1644          } catch (dml_missing_record_exception $e) {
1645              // create new exception which will contain correct table name
1646              throw new dml_missing_record_exception($table, $e->sql, $e->params);
1647          }
1648      }
1649  
1650      /**
1651       * Get a single database record as an object using a SQL statement.
1652       *
1653       * The SQL statement should normally only return one record.
1654       * It is recommended to use get_records_sql() if more matches possible!
1655       *
1656       * @param string $sql The SQL string you wish to be executed, should normally only return one record.
1657       * @param array $params array of sql parameters
1658       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1659       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1660       *                        MUST_EXIST means throw exception if no record or multiple records found
1661       * @return mixed a fieldset object containing the first matching record, false or exception if error not found depending on mode
1662       * @throws dml_exception A DML specific exception is thrown for any errors.
1663       */
1664      public function get_record_sql($sql, array $params=null, $strictness=IGNORE_MISSING) {
1665          $strictness = (int)$strictness; // we support true/false for BC reasons too
1666          if ($strictness == IGNORE_MULTIPLE) {
1667              $count = 1;
1668          } else {
1669              $count = 0;
1670          }
1671          if (!$records = $this->get_records_sql($sql, $params, 0, $count)) {
1672              // not found
1673              if ($strictness == MUST_EXIST) {
1674                  throw new dml_missing_record_exception('', $sql, $params);
1675              }
1676              return false;
1677          }
1678  
1679          if (count($records) > 1) {
1680              if ($strictness == MUST_EXIST) {
1681                  throw new dml_multiple_records_exception($sql, $params);
1682              }
1683              debugging('Error: mdb->get_record() found more than one record!');
1684          }
1685  
1686          $return = reset($records);
1687          return $return;
1688      }
1689  
1690      /**
1691       * Get a single field value from a table record where all the given conditions met.
1692       *
1693       * @param string $table the table to query.
1694       * @param string $return the field to return the value of.
1695       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1696       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1697       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1698       *                        MUST_EXIST means throw exception if no record or multiple records found
1699       * @return mixed the specified value false if not found
1700       * @throws dml_exception A DML specific exception is thrown for any errors.
1701       */
1702      public function get_field($table, $return, array $conditions, $strictness=IGNORE_MISSING) {
1703          list($select, $params) = $this->where_clause($table, $conditions);
1704          return $this->get_field_select($table, $return, $select, $params, $strictness);
1705      }
1706  
1707      /**
1708       * Get a single field value from a table record which match a particular WHERE clause.
1709       *
1710       * @param string $table the table to query.
1711       * @param string $return the field to return the value of.
1712       * @param string $select A fragment of SQL to be used in a where clause returning one row with one column
1713       * @param array $params array of sql parameters
1714       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1715       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1716       *                        MUST_EXIST means throw exception if no record or multiple records found
1717       * @return mixed the specified value false if not found
1718       * @throws dml_exception A DML specific exception is thrown for any errors.
1719       */
1720      public function get_field_select($table, $return, $select, array $params=null, $strictness=IGNORE_MISSING) {
1721          if ($select) {
1722              $select = "WHERE $select";
1723          }
1724          try {
1725              return $this->get_field_sql("SELECT $return FROM {" . $table . "} $select", $params, $strictness);
1726          } catch (dml_missing_record_exception $e) {
1727              // create new exception which will contain correct table name
1728              throw new dml_missing_record_exception($table, $e->sql, $e->params);
1729          }
1730      }
1731  
1732      /**
1733       * Get a single field value (first field) using a SQL statement.
1734       *
1735       * @param string $sql The SQL query returning one row with one column
1736       * @param array $params array of sql parameters
1737       * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1738       *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1739       *                        MUST_EXIST means throw exception if no record or multiple records found
1740       * @return mixed the specified value false if not found
1741       * @throws dml_exception A DML specific exception is thrown for any errors.
1742       */
1743      public function get_field_sql($sql, array $params=null, $strictness=IGNORE_MISSING) {
1744          if (!$record = $this->get_record_sql($sql, $params, $strictness)) {
1745              return false;
1746          }
1747  
1748          $record = (array)$record;
1749          return reset($record); // first column
1750      }
1751  
1752      /**
1753       * Selects records and return values of chosen field as an array which match a particular WHERE clause.
1754       *
1755       * @param string $table the table to query.
1756       * @param string $return the field we are intered in
1757       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1758       * @param array $params array of sql parameters
1759       * @return array of values
1760       * @throws dml_exception A DML specific exception is thrown for any errors.
1761       */
1762      public function get_fieldset_select($table, $return, $select, array $params=null) {
1763          if ($select) {
1764              $select = "WHERE $select";
1765          }
1766          return $this->get_fieldset_sql("SELECT $return FROM {" . $table . "} $select", $params);
1767      }
1768  
1769      /**
1770       * Selects records and return values (first field) as an array using a SQL statement.
1771       *
1772       * @param string $sql The SQL query
1773       * @param array $params array of sql parameters
1774       * @return array of values
1775       * @throws dml_exception A DML specific exception is thrown for any errors.
1776       */
1777      public abstract function get_fieldset_sql($sql, array $params=null);
1778  
1779      /**
1780       * Insert new record into database, as fast as possible, no safety checks, lobs not supported.
1781       * @param string $table name
1782       * @param mixed $params data record as object or array
1783       * @param bool $returnid Returns id of inserted record.
1784       * @param bool $bulk true means repeated inserts expected
1785       * @param bool $customsequence true if 'id' included in $params, disables $returnid
1786       * @return bool|int true or new id
1787       * @throws dml_exception A DML specific exception is thrown for any errors.
1788       */
1789      public abstract function insert_record_raw($table, $params, $returnid=true, $bulk=false, $customsequence=false);
1790  
1791      /**
1792       * Insert a record into a table and return the "id" field if required.
1793       *
1794       * Some conversions and safety checks are carried out. Lobs are supported.
1795       * If the return ID isn't required, then this just reports success as true/false.
1796       * $data is an object containing needed data
1797       * @param string $table The database table to be inserted into
1798       * @param object|array $dataobject A data object with values for one or more fields in the record
1799       * @param bool $returnid Should the id of the newly created record entry be returned? If this option is not requested then true/false is returned.
1800       * @param bool $bulk Set to true is multiple inserts are expected
1801       * @return bool|int true or new id
1802       * @throws dml_exception A DML specific exception is thrown for any errors.
1803       */
1804      public abstract function insert_record($table, $dataobject, $returnid=true, $bulk=false);
1805  
1806      /**
1807       * Insert multiple records into database as fast as possible.
1808       *
1809       * Order of inserts is maintained, but the operation is not atomic,
1810       * use transactions if necessary.
1811       *
1812       * This method is intended for inserting of large number of small objects,
1813       * do not use for huge objects with text or binary fields.
1814       *
1815       * @since Moodle 2.7
1816       *
1817       * @param string $table  The database table to be inserted into
1818       * @param array|Traversable $dataobjects list of objects to be inserted, must be compatible with foreach
1819       * @return void does not return new record ids
1820       *
1821       * @throws coding_exception if data objects have different structure
1822       * @throws dml_exception A DML specific exception is thrown for any errors.
1823       */
1824      public function insert_records($table, $dataobjects) {
1825          if (!is_array($dataobjects) and !($dataobjects instanceof Traversable)) {
1826              throw new coding_exception('insert_records() passed non-traversable object');
1827          }
1828  
1829          $fields = null;
1830          // Note: override in driver if there is a faster way.
1831          foreach ($dataobjects as $dataobject) {
1832              if (!is_array($dataobject) and !is_object($dataobject)) {
1833                  throw new coding_exception('insert_records() passed invalid record object');
1834              }
1835              $dataobject = (array)$dataobject;
1836              if ($fields === null) {
1837                  $fields = array_keys($dataobject);
1838              } else if ($fields !== array_keys($dataobject)) {
1839                  throw new coding_exception('All dataobjects in insert_records() must have the same structure!');
1840              }
1841              $this->insert_record($table, $dataobject, false);
1842          }
1843      }
1844  
1845      /**
1846       * Import a record into a table, id field is required.
1847       * Safety checks are NOT carried out. Lobs are supported.
1848       *
1849       * @param string $table name of database table to be inserted into
1850       * @param object $dataobject A data object with values for one or more fields in the record
1851       * @return bool true
1852       * @throws dml_exception A DML specific exception is thrown for any errors.
1853       */
1854      public abstract function import_record($table, $dataobject);
1855  
1856      /**
1857       * Update record in database, as fast as possible, no safety checks, lobs not supported.
1858       * @param string $table name
1859       * @param mixed $params data record as object or array
1860       * @param bool $bulk True means repeated updates expected.
1861       * @return bool true
1862       * @throws dml_exception A DML specific exception is thrown for any errors.
1863       */
1864      public abstract function update_record_raw($table, $params, $bulk=false);
1865  
1866      /**
1867       * Update a record in a table
1868       *
1869       * $dataobject is an object containing needed data
1870       * Relies on $dataobject having a variable "id" to
1871       * specify the record to update
1872       *
1873       * @param string $table The database table to be checked against.
1874       * @param object $dataobject An object with contents equal to fieldname=>fieldvalue. Must have an entry for 'id' to map to the table specified.
1875       * @param bool $bulk True means repeated updates expected.
1876       * @return bool true
1877       * @throws dml_exception A DML specific exception is thrown for any errors.
1878       */
1879      public abstract function update_record($table, $dataobject, $bulk=false);
1880  
1881      /**
1882       * Set a single field in every table record where all the given conditions met.
1883       *
1884       * @param string $table The database table to be checked against.
1885       * @param string $newfield the field to set.
1886       * @param string $newvalue the value to set the field to.
1887       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1888       * @return bool true
1889       * @throws dml_exception A DML specific exception is thrown for any errors.
1890       */
1891      public function set_field($table, $newfield, $newvalue, array $conditions=null) {
1892          list($select, $params) = $this->where_clause($table, $conditions);
1893          return $this->set_field_select($table, $newfield, $newvalue, $select, $params);
1894      }
1895  
1896      /**
1897       * Set a single field in every table record which match a particular WHERE clause.
1898       *
1899       * @param string $table The database table to be checked against.
1900       * @param string $newfield the field to set.
1901       * @param string $newvalue the value to set the field to.
1902       * @param string $select A fragment of SQL to be used in a where clause in the SQL call.
1903       * @param array $params array of sql parameters
1904       * @return bool true
1905       * @throws dml_exception A DML specific exception is thrown for any errors.
1906       */
1907      public abstract function set_field_select($table, $newfield, $newvalue, $select, array $params=null);
1908  
1909  
1910      /**
1911       * Count the records in a table where all the given conditions met.
1912       *
1913       * @param string $table The table to query.
1914       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1915       * @return int The count of records returned from the specified criteria.
1916       * @throws dml_exception A DML specific exception is thrown for any errors.
1917       */
1918      public function count_records($table, array $conditions=null) {
1919          list($select, $params) = $this->where_clause($table, $conditions);
1920          return $this->count_records_select($table, $select, $params);
1921      }
1922  
1923      /**
1924       * Count the records in a table which match a particular WHERE clause.
1925       *
1926       * @param string $table The database table to be checked against.
1927       * @param string $select A fragment of SQL to be used in a WHERE clause in the SQL call.
1928       * @param array $params array of sql parameters
1929       * @param string $countitem The count string to be used in the SQL call. Default is COUNT('x').
1930       * @return int The count of records returned from the specified criteria.
1931       * @throws dml_exception A DML specific exception is thrown for any errors.
1932       */
1933      public function count_records_select($table, $select, array $params=null, $countitem="COUNT('x')") {
1934          if ($select) {
1935              $select = "WHERE $select";
1936          }
1937          return $this->count_records_sql("SELECT $countitem FROM {" . $table . "} $select", $params);
1938      }
1939  
1940      /**
1941       * Get the result of a SQL SELECT COUNT(...) query.
1942       *
1943       * Given a query that counts rows, return that count. (In fact,
1944       * given any query, return the first field of the first record
1945       * returned. However, this method should only be used for the
1946       * intended purpose.) If an error occurs, 0 is returned.
1947       *
1948       * @param string $sql The SQL string you wish to be executed.
1949       * @param array $params array of sql parameters
1950       * @return int the count
1951       * @throws dml_exception A DML specific exception is thrown for any errors.
1952       */
1953      public function count_records_sql($sql, array $params=null) {
1954          $count = $this->get_field_sql($sql, $params);
1955          if ($count === false or !is_number($count) or $count < 0) {
1956              throw new coding_exception("count_records_sql() expects the first field to contain non-negative number from COUNT(), '$count' found instead.");
1957          }
1958          return (int)$count;
1959      }
1960  
1961      /**
1962       * Test whether a record exists in a table where all the given conditions met.
1963       *
1964       * @param string $table The table to check.
1965       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
1966       * @return bool true if a matching record exists, else false.
1967       * @throws dml_exception A DML specific exception is thrown for any errors.
1968       */
1969      public function record_exists($table, array $conditions) {
1970          list($select, $params) = $this->where_clause($table, $conditions);
1971          return $this->record_exists_select($table, $select, $params);
1972      }
1973  
1974      /**
1975       * Test whether any records exists in a table which match a particular WHERE clause.
1976       *
1977       * @param string $table The database table to be checked against.
1978       * @param string $select A fragment of SQL to be used in a WHERE clause in the SQL call.
1979       * @param array $params array of sql parameters
1980       * @return bool true if a matching record exists, else false.
1981       * @throws dml_exception A DML specific exception is thrown for any errors.
1982       */
1983      public function record_exists_select($table, $select, array $params=null) {
1984          if ($select) {
1985              $select = "WHERE $select";
1986          }
1987          return $this->record_exists_sql("SELECT 'x' FROM {" . $table . "} $select", $params);
1988      }
1989  
1990      /**
1991       * Test whether a SQL SELECT statement returns any records.
1992       *
1993       * This function returns true if the SQL statement executes
1994       * without any errors and returns at least one record.
1995       *
1996       * @param string $sql The SQL statement to execute.
1997       * @param array $params array of sql parameters
1998       * @return bool true if the SQL executes without errors and returns at least one record.
1999       * @throws dml_exception A DML specific exception is thrown for any errors.
2000       */
2001      public function record_exists_sql($sql, array $params=null) {
2002          $mrs = $this->get_recordset_sql($sql, $params, 0, 1);
2003          $return = $mrs->valid();
2004          $mrs->close();
2005          return $return;
2006      }
2007  
2008      /**
2009       * Delete the records from a table where all the given conditions met.
2010       * If conditions not specified, table is truncated.
2011       *
2012       * @param string $table the table to delete from.
2013       * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
2014       * @return bool true.
2015       * @throws dml_exception A DML specific exception is thrown for any errors.
2016       */
2017      public function delete_records($table, array $conditions=null) {
2018          // truncate is drop/create (DDL), not transactional safe,
2019          // so we don't use the shortcut within them. MDL-29198
2020          if (is_null($conditions) && empty($this->transactions)) {
2021              return $this->execute("TRUNCATE TABLE {".$table."}");
2022          }
2023          list($select, $params) = $this->where_clause($table, $conditions);
2024          return $this->delete_records_select($table, $select, $params);
2025      }
2026  
2027      /**
2028       * Delete the records from a table where one field match one list of values.
2029       *
2030       * @param string $table the table to delete from.
2031       * @param string $field The field to search
2032       * @param array $values array of values
2033       * @return bool true.
2034       * @throws dml_exception A DML specific exception is thrown for any errors.
2035       */
2036      public function delete_records_list($table, $field, array $values) {
2037          list($select, $params) = $this->where_clause_list($field, $values);
2038          return $this->delete_records_select($table, $select, $params);
2039      }
2040  
2041      /**
2042       * Deletes records from a table using a subquery. The subquery should return a list of values
2043       * in a single column, which match one field from the table being deleted.
2044       *
2045       * The $alias parameter must be set to the name of the single column in your subquery result
2046       * (e.g. if the subquery is 'SELECT id FROM whatever', then it should be 'id'). This is not
2047       * needed on most databases, but MySQL requires it.
2048       *
2049       * (On database where the subquery is inefficient, it is implemented differently.)
2050       *
2051       * @param string $table Table to delete from
2052       * @param string $field Field in table to match
2053       * @param string $alias Name of single column in subquery e.g. 'id'
2054       * @param string $subquery Subquery that will return values of the field to delete
2055       * @param array $params Parameters for subquery
2056       * @throws dml_exception If there is any error
2057       * @since Moodle 3.10
2058       */
2059      public function delete_records_subquery(string $table, string $field, string $alias,
2060              string $subquery, array $params = []): void {
2061          $this->delete_records_select($table, $field . ' IN (' . $subquery . ')', $params);
2062      }
2063  
2064      /**
2065       * Delete one or more records from a table which match a particular WHERE clause.
2066       *
2067       * @param string $table The database table to be checked against.
2068       * @param string $select A fragment of SQL to be used in a where clause in the SQL call (used to define the selection criteria).
2069       * @param array $params array of sql parameters
2070       * @return bool true.
2071       * @throws dml_exception A DML specific exception is thrown for any errors.
2072       */
2073      public abstract function delete_records_select($table, $select, array $params=null);
2074  
2075      /**
2076       * Returns the FROM clause required by some DBs in all SELECT statements.
2077       *
2078       * To be used in queries not having FROM clause to provide cross_db
2079       * Most DBs don't need it, hence the default is ''
2080       * @return string
2081       */
2082      public function sql_null_from_clause() {
2083          return '';
2084      }
2085  
2086      /**
2087       * Returns the SQL text to be used in order to perform one bitwise AND operation
2088       * between 2 integers.
2089       *
2090       * NOTE: The SQL result is a number and can not be used directly in
2091       *       SQL condition, please compare it to some number to get a bool!!
2092       *
2093       * @param int $int1 First integer in the operation.
2094       * @param int $int2 Second integer in the operation.
2095       * @return string The piece of SQL code to be used in your statement.
2096       */
2097      public function sql_bitand($int1, $int2) {
2098          return '((' . $int1 . ') & (' . $int2 . '))';
2099      }
2100  
2101      /**
2102       * Returns the SQL text to be used in order to perform one bitwise NOT operation
2103       * with 1 integer.
2104       *
2105       * @param int $int1 The operand integer in the operation.
2106       * @return string The piece of SQL code to be used in your statement.
2107       */
2108      public function sql_bitnot($int1) {
2109          return '(~(' . $int1 . '))';
2110      }
2111  
2112      /**
2113       * Returns the SQL text to be used in order to perform one bitwise OR operation
2114       * between 2 integers.
2115       *
2116       * NOTE: The SQL result is a number and can not be used directly in
2117       *       SQL condition, please compare it to some number to get a bool!!
2118       *
2119       * @param int $int1 The first operand integer in the operation.
2120       * @param int $int2 The second operand integer in the operation.
2121       * @return string The piece of SQL code to be used in your statement.
2122       */
2123      public function sql_bitor($int1, $int2) {
2124          return '((' . $int1 . ') | (' . $int2 . '))';
2125      }
2126  
2127      /**
2128       * Returns the SQL text to be used in order to perform one bitwise XOR operation
2129       * between 2 integers.
2130       *
2131       * NOTE: The SQL result is a number and can not be used directly in
2132       *       SQL condition, please compare it to some number to get a bool!!
2133       *
2134       * @param int $int1 The first operand integer in the operation.
2135       * @param int $int2 The second operand integer in the operation.
2136       * @return string The piece of SQL code to be used in your statement.
2137       */
2138      public function sql_bitxor($int1, $int2) {
2139          return '((' . $int1 . ') ^ (' . $int2 . '))';
2140      }
2141  
2142      /**
2143       * Returns the SQL text to be used in order to perform module '%'
2144       * operation - remainder after division
2145       *
2146       * @param int $int1 The first operand integer in the operation.
2147       * @param int $int2 The second operand integer in the operation.
2148       * @return string The piece of SQL code to be used in your statement.
2149       */
2150      public function sql_modulo($int1, $int2) {
2151          return '((' . $int1 . ') % (' . $int2 . '))';
2152      }
2153  
2154      /**
2155       * Returns the cross db correct CEIL (ceiling) expression applied to fieldname.
2156       * note: Most DBs use CEIL(), hence it's the default here.
2157       *
2158       * @param string $fieldname The field (or expression) we are going to ceil.
2159       * @return string The piece of SQL code to be used in your ceiling statement.
2160       */
2161      public function sql_ceil($fieldname) {
2162          return ' CEIL(' . $fieldname . ')';
2163      }
2164  
2165      /**
2166       * Returns the SQL to be used in order to CAST one CHAR column to INTEGER.
2167       *
2168       * Be aware that the CHAR column you're trying to cast contains really
2169       * int values or the RDBMS will throw an error!
2170       *
2171       * @param string $fieldname The name of the field to be casted.
2172       * @param bool $text Specifies if the original column is one TEXT (CLOB) column (true). Defaults to false.
2173       * @return string The piece of SQL code to be used in your statement.
2174       */
2175      public function sql_cast_char2int($fieldname, $text=false) {
2176          return ' ' . $fieldname . ' ';
2177      }
2178  
2179      /**
2180       * Returns the SQL to be used in order to CAST one CHAR column to REAL number.
2181       *
2182       * Be aware that the CHAR column you're trying to cast contains really
2183       * numbers or the RDBMS will throw an error!
2184       *
2185       * @param string $fieldname The name of the field to be casted.
2186       * @param bool $text Specifies if the original column is one TEXT (CLOB) column (true). Defaults to false.
2187       * @return string The piece of SQL code to be used in your statement.
2188       */
2189      public function sql_cast_char2real($fieldname, $text=false) {
2190          return ' ' . $fieldname . ' ';
2191      }
2192  
2193      /**
2194       * Returns the SQL to be used in order to an UNSIGNED INTEGER column to SIGNED.
2195       *
2196       * (Only MySQL needs this. MySQL things that 1 * -1 = 18446744073709551615
2197       * if the 1 comes from an unsigned column).
2198       *
2199       * @deprecated since 2.3
2200       * @param string $fieldname The name of the field to be cast
2201       * @return string The piece of SQL code to be used in your statement.
2202       */
2203      public function sql_cast_2signed($fieldname) {
2204          return ' ' . $fieldname . ' ';
2205      }
2206  
2207      /**
2208       * Returns the SQL text to be used to compare one TEXT (clob) column with
2209       * one varchar column, because some RDBMS doesn't support such direct
2210       * comparisons.
2211       *
2212       * @param string $fieldname The name of the TEXT field we need to order by
2213       * @param int $numchars Number of chars to use for the ordering (defaults to 32).
2214       * @return string The piece of SQL code to be used in your statement.
2215       */
2216      public function sql_compare_text($fieldname, $numchars=32) {
2217          return $this->sql_order_by_text($fieldname, $numchars);
2218      }
2219  
2220      /**
2221       * Returns an equal (=) or not equal (<>) part of a query.
2222       *
2223       * Note the use of this method may lead to slower queries (full scans) so
2224       * use it only when needed and against already reduced data sets.
2225       *
2226       * @since Moodle 3.2
2227       *
2228       * @param string $fieldname Usually the name of the table column.
2229       * @param string $param Usually the bound query parameter (?, :named).
2230       * @param bool $casesensitive Use case sensitive search when set to true (default).
2231       * @param bool $accentsensitive Use accent sensitive search when set to true (default). (not all databases support accent insensitive)
2232       * @param bool $notequal True means not equal (<>)
2233       * @return string The SQL code fragment.
2234       */
2235      public function sql_equal($fieldname, $param, $casesensitive = true, $accentsensitive = true, $notequal = false) {
2236          // Note that, by default, it's assumed that the correct sql equal operations are
2237          // case sensitive. Only databases not observing this behavior must override the method.
2238          // Also, accent sensitiveness only will be handled by databases supporting it.
2239          $equalop = $notequal ? '<>' : '=';
2240          if ($casesensitive) {
2241              return "$fieldname $equalop $param";
2242          } else {
2243              return "LOWER($fieldname) $equalop LOWER($param)";
2244          }
2245      }
2246  
2247      /**
2248       * Returns 'LIKE' part of a query.
2249       *
2250       * @param string $fieldname Usually the name of the table column.
2251       * @param string $param Usually the bound query parameter (?, :named).
2252       * @param bool $casesensitive Use case sensitive search when set to true (default).
2253       * @param bool $accentsensitive Use accent sensitive search when set to true (default). (not all databases support accent insensitive)
2254       * @param bool $notlike True means "NOT LIKE".
2255       * @param string $escapechar The escape char for '%' and '_'.
2256       * @return string The SQL code fragment.
2257       */
2258      public function sql_like($fieldname, $param, $casesensitive = true, $accentsensitive = true, $notlike = false, $escapechar = '\\') {
2259          if (strpos($param, '%') !== false) {
2260              debugging('Potential SQL injection detected, sql_like() expects bound parameters (? or :named)');
2261          }
2262          $LIKE = $notlike ? 'NOT LIKE' : 'LIKE';
2263          // by default ignore any sensitiveness - each database does it in a different way
2264          return "$fieldname $LIKE $param ESCAPE '$escapechar'";
2265      }
2266  
2267      /**
2268       * Escape sql LIKE special characters like '_' or '%'.
2269       * @param string $text The string containing characters needing escaping.
2270       * @param string $escapechar The desired escape character, defaults to '\\'.
2271       * @return string The escaped sql LIKE string.
2272       */
2273      public function sql_like_escape($text, $escapechar = '\\') {
2274          $text = str_replace('_', $escapechar.'_', $text);
2275          $text = str_replace('%', $escapechar.'%', $text);
2276          return $text;
2277      }
2278  
2279      /**
2280       * Returns the proper SQL to do CONCAT between the elements(fieldnames) passed.
2281       *
2282       * This function accepts variable number of string parameters.
2283       * All strings/fieldnames will used in the SQL concatenate statement generated.
2284       *
2285       * @return string The SQL to concatenate strings passed in.
2286       * @uses func_get_args()  and thus parameters are unlimited OPTIONAL number of additional field names.
2287       */
2288      public abstract function sql_concat();
2289  
2290      /**
2291       * Returns the proper SQL to do CONCAT between the elements passed
2292       * with a given separator
2293       *
2294       * @param string $separator The separator desired for the SQL concatenating $elements.
2295       * @param array  $elements The array of strings to be concatenated.
2296       * @return string The SQL to concatenate the strings.
2297       */
2298      public abstract function sql_concat_join($separator="' '", $elements=array());
2299  
2300      /**
2301       * Return SQL for performing group concatenation on given field/expression
2302       *
2303       * @param string $field Table field or SQL expression to be concatenated
2304       * @param string $separator The separator desired between each concatetated field
2305       * @param string $sort Ordering of the concatenated field
2306       * @return string
2307       */
2308      public abstract function sql_group_concat(string $field, string $separator = ', ', string $sort = ''): string;
2309  
2310      /**
2311       * Returns the proper SQL (for the dbms in use) to concatenate $firstname and $lastname
2312       *
2313       * @todo MDL-31233 This may not be needed here.
2314       *
2315       * @param string $first User's first name (default:'firstname').
2316       * @param string $last User's last name (default:'lastname').
2317       * @return string The SQL to concatenate strings.
2318       */
2319      function sql_fullname($first='firstname', $last='lastname') {
2320          return $this->sql_concat($first, "' '", $last);
2321      }
2322  
2323      /**
2324       * Returns the SQL text to be used to order by one TEXT (clob) column, because
2325       * some RDBMS doesn't support direct ordering of such fields.
2326       *
2327       * Note that the use or queries being ordered by TEXT columns must be minimised,
2328       * because it's really slooooooow.
2329       *
2330       * @param string $fieldname The name of the TEXT field we need to order by.
2331       * @param int $numchars The number of chars to use for the ordering (defaults to 32).
2332       * @return string The piece of SQL code to be used in your statement.
2333       */
2334      public function sql_order_by_text($fieldname, $numchars=32) {
2335          return $fieldname;
2336      }
2337  
2338      /**
2339       * Returns the SQL text to be used to calculate the length in characters of one expression.
2340       * @param string $fieldname The fieldname/expression to calculate its length in characters.
2341       * @return string the piece of SQL code to be used in the statement.
2342       */
2343      public function sql_length($fieldname) {
2344          return ' LENGTH(' . $fieldname . ')';
2345      }
2346  
2347      /**
2348       * Returns the proper substr() SQL text used to extract substrings from DB
2349       * NOTE: this was originally returning only function name
2350       *
2351       * @param string $expr Some string field, no aggregates.
2352       * @param mixed $start Integer or expression evaluating to integer (1 based value; first char has index 1)
2353       * @param mixed $length Optional integer or expression evaluating to integer.
2354       * @return string The sql substring extraction fragment.
2355       */
2356      public function sql_substr($expr, $start, $length=false) {
2357          if (count(func_get_args()) < 2) {
2358              throw new coding_exception('moodle_database::sql_substr() requires at least two parameters', 'Originally this function was only returning name of SQL substring function, it now requires all parameters.');
2359          }
2360          if ($length === false) {
2361              return "SUBSTR($expr, $start)";
2362          } else {
2363              return "SUBSTR($expr, $start, $length)";
2364          }
2365      }
2366  
2367      /**
2368       * Returns the SQL for returning searching one string for the location of another.
2369       *
2370       * Note, there is no guarantee which order $needle, $haystack will be in
2371       * the resulting SQL so when using this method, and both arguments contain
2372       * placeholders, you should use named placeholders.
2373       *
2374       * @param string $needle the SQL expression that will be searched for.
2375       * @param string $haystack the SQL expression that will be searched in.
2376       * @return string The required searching SQL part.
2377       */
2378      public function sql_position($needle, $haystack) {
2379          // Implementation using standard SQL.
2380          return "POSITION(($needle) IN ($haystack))";
2381      }
2382  
2383      /**
2384       * This used to return empty string replacement character.
2385       *
2386       * @deprecated use bound parameter with empty string instead
2387       *
2388       * @return string An empty string.
2389       */
2390      function sql_empty() {
2391          debugging("sql_empty() is deprecated, please use empty string '' as sql parameter value instead", DEBUG_DEVELOPER);
2392          return '';
2393      }
2394  
2395      /**
2396       * Returns the proper SQL to know if one field is empty.
2397       *
2398       * Note that the function behavior strongly relies on the
2399       * parameters passed describing the field so, please,  be accurate
2400       * when specifying them.
2401       *
2402       * Also, note that this function is not suitable to look for
2403       * fields having NULL contents at all. It's all for empty values!
2404       *
2405       * This function should be applied in all the places where conditions of
2406       * the type:
2407       *
2408       *     ... AND fieldname = '';
2409       *
2410       * are being used. Final result for text fields should be:
2411       *
2412       *     ... AND ' . sql_isempty('tablename', 'fieldname', true/false, true);
2413       *
2414       * and for varchar fields result should be:
2415       *
2416       *    ... AND fieldname = :empty; "; $params['empty'] = '';
2417       *
2418       * (see parameters description below)
2419       *
2420       * @param string $tablename Name of the table (without prefix). Not used for now but can be
2421       *                          necessary in the future if we want to use some introspection using
2422       *                          meta information against the DB. /// TODO ///
2423       * @param string $fieldname Name of the field we are going to check
2424       * @param bool $nullablefield For specifying if the field is nullable (true) or no (false) in the DB.
2425       * @param bool $textfield For specifying if it is a text (also called clob) field (true) or a varchar one (false)
2426       * @return string the sql code to be added to check for empty values
2427       */
2428      public function sql_isempty($tablename, $fieldname, $nullablefield, $textfield) {
2429          return " ($fieldname = '') ";
2430      }
2431  
2432      /**
2433       * Returns the proper SQL to know if one field is not empty.
2434       *
2435       * Note that the function behavior strongly relies on the
2436       * parameters passed describing the field so, please,  be accurate
2437       * when specifying them.
2438       *
2439       * This function should be applied in all the places where conditions of
2440       * the type:
2441       *
2442       *     ... AND fieldname != '';
2443       *
2444       * are being used. Final result for text fields should be:
2445       *
2446       *     ... AND ' . sql_isnotempty('tablename', 'fieldname', true/false, true/false);
2447       *
2448       * and for varchar fields result should be:
2449       *
2450       *    ... AND fieldname != :empty; "; $params['empty'] = '';
2451       *
2452       * (see parameters description below)
2453       *
2454       * @param string $tablename Name of the table (without prefix). This is not used for now but can be
2455       *                          necessary in the future if we want to use some introspection using
2456       *                          meta information against the DB.
2457       * @param string $fieldname The name of the field we are going to check.
2458       * @param bool $nullablefield Specifies if the field is nullable (true) or not (false) in the DB.
2459       * @param bool $textfield Specifies if it is a text (also called clob) field (true) or a varchar one (false).
2460       * @return string The sql code to be added to check for non empty values.
2461       */
2462      public function sql_isnotempty($tablename, $fieldname, $nullablefield, $textfield) {
2463          return ' ( NOT ' . $this->sql_isempty($tablename, $fieldname, $nullablefield, $textfield) . ') ';
2464      }
2465  
2466      /**
2467       * Returns true if this database driver supports regex syntax when searching.
2468       * @return bool True if supported.
2469       */
2470      public function sql_regex_supported() {
2471          return false;
2472      }
2473  
2474      /**
2475       * Returns the driver specific syntax (SQL part) for matching regex positively or negatively (inverted matching).
2476       * Eg: 'REGEXP':'NOT REGEXP' or '~*' : '!~*'
2477       *
2478       * @param bool $positivematch
2479       * @param bool $casesensitive
2480       * @return string or empty if not supported
2481       */
2482      public function sql_regex($positivematch = true, $casesensitive = false) {
2483          return '';
2484      }
2485  
2486      /**
2487       * Returns the word-beginning boundary marker if this database driver supports regex syntax when searching.
2488       * @return string The word-beginning boundary marker. Otherwise, an empty string.
2489       */
2490      public function sql_regex_get_word_beginning_boundary_marker() {
2491          if ($this->sql_regex_supported()) {
2492              return '[[:<:]]';
2493          }
2494  
2495          return '';
2496      }
2497  
2498      /**
2499       * Returns the word-end boundary marker if this database driver supports regex syntax when searching.
2500       * @return string The word-end boundary marker. Otherwise, an empty string.
2501       */
2502      public function sql_regex_get_word_end_boundary_marker() {
2503          if ($this->sql_regex_supported()) {
2504              return '[[:>:]]';
2505          }
2506  
2507          return '';
2508      }
2509  
2510      /**
2511       * Returns the SQL that allows to find intersection of two or more queries
2512       *
2513       * @since Moodle 2.8
2514       *
2515       * @param array $selects array of SQL select queries, each of them only returns fields with the names from $fields
2516       * @param string $fields comma-separated list of fields (used only by some DB engines)
2517       * @return string SQL query that will return only values that are present in each of selects
2518       */
2519      public function sql_intersect($selects, $fields) {
2520          if (!count($selects)) {
2521              throw new coding_exception('sql_intersect() requires at least one element in $selects');
2522          } else if (count($selects) == 1) {
2523              return $selects[0];
2524          }
2525          static $aliascnt = 0;
2526          $rv = '('.$selects[0].')';
2527          for ($i = 1; $i < count($selects); $i++) {
2528              $rv .= " INTERSECT (".$selects[$i].')';
2529          }
2530          return $rv;
2531      }
2532  
2533      /**
2534       * Does this driver support tool_replace?
2535       *
2536       * @since Moodle 2.6.1
2537       * @return bool
2538       */
2539      public function replace_all_text_supported() {
2540          return false;
2541      }
2542  
2543      /**
2544       * Replace given text in all rows of column.
2545       *
2546       * @since Moodle 2.6.1
2547       * @param string $table name of the table
2548       * @param database_column_info $column
2549       * @param string $search
2550       * @param string $replace
2551       */
2552      public function replace_all_text($table, database_column_info $column, $search, $replace) {
2553          if (!$this->replace_all_text_supported()) {
2554              return;
2555          }
2556  
2557          // NOTE: override this methods if following standard compliant SQL
2558          //       does not work for your driver.
2559  
2560          // Enclose the column name by the proper quotes if it's a reserved word.
2561          $columnname = $this->get_manager()->generator->getEncQuoted($column->name);
2562  
2563          $searchsql = $this->sql_like($columnname, '?');
2564          $searchparam = '%'.$this->sql_like_escape($search).'%';
2565  
2566          $sql = "UPDATE {".$table."}
2567                         SET $columnname = REPLACE($columnname, ?, ?)
2568                       WHERE $searchsql";
2569  
2570          if ($column->meta_type === 'X') {
2571              $this->execute($sql, array($search, $replace, $searchparam));
2572  
2573          } else if ($column->meta_type === 'C') {
2574              if (core_text::strlen($search) < core_text::strlen($replace)) {
2575                  $colsize = $column->max_length;
2576                  $sql = "UPDATE {".$table."}
2577                         SET $columnname = " . $this->sql_substr("REPLACE(" . $columnname . ", ?, ?)", 1, $colsize) . "
2578                       WHERE $searchsql";
2579              }
2580              $this->execute($sql, array($search, $replace, $searchparam));
2581          }
2582      }
2583  
2584      /**
2585       * Analyze the data in temporary tables to force statistics collection after bulk data loads.
2586       *
2587       * @return void
2588       */
2589      public function update_temp_table_stats() {
2590          $this->temptables->update_stats();
2591      }
2592  
2593      /**
2594       * Checks and returns true if transactions are supported.
2595       *
2596       * It is not responsible to run productions servers
2597       * on databases without transaction support ;-)
2598       *
2599       * Override in driver if needed.
2600       *
2601       * @return bool
2602       */
2603      protected function transactions_supported() {
2604          // protected for now, this might be changed to public if really necessary
2605          return true;
2606      }
2607  
2608      /**
2609       * Returns true if a transaction is in progress.
2610       * @return bool
2611       */
2612      public function is_transaction_started() {
2613          return !empty($this->transactions);
2614      }
2615  
2616      /**
2617       * This is a test that throws an exception if transaction in progress.
2618       * This test does not force rollback of active transactions.
2619       * @return void
2620       * @throws dml_transaction_exception if stansaction active
2621       */
2622      public function transactions_forbidden() {
2623          if ($this->is_transaction_started()) {
2624              throw new dml_transaction_exception('This code can not be excecuted in transaction');
2625          }
2626      }
2627  
2628      /**
2629       * On DBs that support it, switch to transaction mode and begin a transaction
2630       * you'll need to ensure you call allow_commit() on the returned object
2631       * or your changes *will* be lost.
2632       *
2633       * this is _very_ useful for massive updates
2634       *
2635       * Delegated database transactions can be nested, but only one actual database
2636       * transaction is used for the outer-most delegated transaction. This method
2637       * returns a transaction object which you should keep until the end of the
2638       * delegated transaction. The actual database transaction will
2639       * only be committed if all the nested delegated transactions commit
2640       * successfully. If any part of the transaction rolls back then the whole
2641       * thing is rolled back.
2642       *
2643       * @return moodle_transaction
2644       */
2645      public function start_delegated_transaction() {
2646          $transaction = new moodle_transaction($this);
2647          $this->transactions[] = $transaction;
2648          if (count($this->transactions) == 1) {
2649              $this->begin_transaction();
2650          }
2651          return $transaction;
2652      }
2653  
2654      /**
2655       * Driver specific start of real database transaction,
2656       * this can not be used directly in code.
2657       * @return void
2658       */
2659      protected abstract function begin_transaction();
2660  
2661      /**
2662       * Indicates delegated transaction finished successfully.
2663       * The real database transaction is committed only if
2664       * all delegated transactions committed.
2665       * @param moodle_transaction $transaction The transaction to commit
2666       * @return void
2667       * @throws dml_transaction_exception Creates and throws transaction related exceptions.
2668       */
2669      public function commit_delegated_transaction(moodle_transaction $transaction) {
2670          if ($transaction->is_disposed()) {
2671              throw new dml_transaction_exception('Transactions already disposed', $transaction);
2672          }
2673          // mark as disposed so that it can not be used again
2674          $transaction->dispose();
2675  
2676          if (empty($this->transactions)) {
2677              throw new dml_transaction_exception('Transaction not started', $transaction);
2678          }
2679  
2680          if ($this->force_rollback) {
2681              throw new dml_transaction_exception('Tried to commit transaction after lower level rollback', $transaction);
2682          }
2683  
2684          if ($transaction !== $this->transactions[count($this->transactions) - 1]) {
2685              // one incorrect commit at any level rollbacks everything
2686              $this->force_rollback = true;
2687              throw new dml_transaction_exception('Invalid transaction commit attempt', $transaction);
2688          }
2689  
2690          if (count($this->transactions) == 1) {
2691              // only commit the top most level
2692              $this->commit_transaction();
2693          }
2694          array_pop($this->transactions);
2695  
2696          if (empty($this->transactions)) {
2697              \core\event\manager::database_transaction_commited();
2698              \core\message\manager::database_transaction_commited();
2699          }
2700      }
2701  
2702      /**
2703       * Driver specific commit of real database transaction,
2704       * this can not be used directly in code.
2705       * @return void
2706       */
2707      protected abstract function commit_transaction();
2708  
2709      /**
2710       * Call when delegated transaction failed, this rolls back
2711       * all delegated transactions up to the top most level.
2712       *
2713       * In many cases you do not need to call this method manually,
2714       * because all open delegated transactions are rolled back
2715       * automatically if exceptions not caught.
2716       *
2717       * @param moodle_transaction $transaction An instance of a moodle_transaction.
2718       * @param Exception|Throwable $e The related exception/throwable to this transaction rollback.
2719       * @return void This does not return, instead the exception passed in will be rethrown.
2720       */
2721      public function rollback_delegated_transaction(moodle_transaction $transaction, $e) {
2722          if (!($e instanceof Exception) && !($e instanceof Throwable)) {
2723              // PHP7 - we catch Throwables in phpunit but can't use that as the type hint in PHP5.
2724              $e = new \coding_exception("Must be given an Exception or Throwable object!");
2725          }
2726          if ($transaction->is_disposed()) {
2727              throw new dml_transaction_exception('Transactions already disposed', $transaction);
2728          }
2729          // mark as disposed so that it can not be used again
2730          $transaction->dispose();
2731  
2732          // one rollback at any level rollbacks everything
2733          $this->force_rollback = true;
2734  
2735          if (empty($this->transactions) or $transaction !== $this->transactions[count($this->transactions) - 1]) {
2736              // this may or may not be a coding problem, better just rethrow the exception,
2737              // because we do not want to loose the original $e
2738              throw $e;
2739          }
2740  
2741          if (count($this->transactions) == 1) {
2742              // only rollback the top most level
2743              $this->rollback_transaction();
2744          }
2745          array_pop($this->transactions);
2746          if (empty($this->transactions)) {
2747              // finally top most level rolled back
2748              $this->force_rollback = false;
2749              \core\event\manager::database_transaction_rolledback();
2750              \core\message\manager::database_transaction_rolledback();
2751          }
2752          throw $e;
2753      }
2754  
2755      /**
2756       * Driver specific abort of real database transaction,
2757       * this can not be used directly in code.
2758       * @return void
2759       */
2760      protected abstract function rollback_transaction();
2761  
2762      /**
2763       * Force rollback of all delegated transaction.
2764       * Does not throw any exceptions and does not log anything.
2765       *
2766       * This method should be used only from default exception handlers and other
2767       * core code.
2768       *
2769       * @return void
2770       */
2771      public function force_transaction_rollback() {
2772          if ($this->transactions) {
2773              try {
2774                  $this->rollback_transaction();
2775              } catch (dml_exception $e) {
2776                  // ignore any sql errors here, the connection might be broken
2777              }
2778          }
2779  
2780          // now enable transactions again
2781          $this->transactions = array();
2782          $this->force_rollback = false;
2783  
2784          \core\event\manager::database_transaction_rolledback();
2785          \core\message\manager::database_transaction_rolledback();
2786      }
2787  
2788      /**
2789       * Is session lock supported in this driver?
2790       * @return bool
2791       */
2792      public function session_lock_supported() {
2793          return false;
2794      }
2795  
2796      /**
2797       * Obtains the session lock.
2798       * @param int $rowid The id of the row with session record.
2799       * @param int $timeout The maximum allowed time to wait for the lock in seconds.
2800       * @return void
2801       * @throws dml_exception A DML specific exception is thrown for any errors.
2802       */
2803      public function get_session_lock($rowid, $timeout) {
2804          $this->used_for_db_sessions = true;
2805      }
2806  
2807      /**
2808       * Releases the session lock.
2809       * @param int $rowid The id of the row with session record.
2810       * @return void
2811       * @throws dml_exception A DML specific exception is thrown for any errors.
2812       */
2813      public function release_session_lock($rowid) {
2814      }
2815  
2816      /**
2817       * Returns the number of reads done by this database.
2818       * @return int Number of reads.
2819       */
2820      public function perf_get_reads() {
2821          return $this->reads;
2822      }
2823  
2824      /**
2825       * Returns whether we want to connect to slave database for read queries.
2826       * @return bool Want read only connection
2827       */
2828      public function want_read_slave(): bool {
2829          return false;
2830      }
2831  
2832      /**
2833       * Returns the number of reads before first write done by this database.
2834       * @return int Number of reads.
2835       */
2836      public function perf_get_reads_slave(): int {
2837          return 0;
2838      }
2839  
2840      /**
2841       * Returns the number of writes done by this database.
2842       * @return int Number of writes.
2843       */
2844      public function perf_get_writes() {
2845          return $this->writes;
2846      }
2847  
2848      /**
2849       * Returns the number of queries done by this database.
2850       * @return int Number of queries.
2851       */
2852      public function perf_get_queries() {
2853          return $this->writes + $this->reads;
2854      }
2855  
2856      /**
2857       * Time waiting for the database engine to finish running all queries.
2858       * @return float Number of seconds with microseconds
2859       */
2860      public function perf_get_queries_time() {
2861          return $this->queriestime;
2862      }
2863  
2864      /**
2865       * Whether the database is able to support full-text search or not.
2866       *
2867       * @return bool
2868       */
2869      public function is_fulltext_search_supported() {
2870          // No support unless specified.
2871          return false;
2872      }
2873  }