Only store currently-existing categories in the categories table

[mediawiki.git] / includes / db / DatabaseMssql.php

<?php
/**
 * This is the MS SQL Server Native database abstraction layer.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup Database
 * @author Joel Penner <a-joelpe at microsoft dot com>
 * @author Chris Pucci <a-cpucci at microsoft dot com>
 * @author Ryan Biesemeyer <v-ryanbi at microsoft dot com>
 * @author Ryan Schmidt <skizzerz at gmail dot com>
 */

/**
 * @ingroup Database
 */
class DatabaseMssql extends Database {
        protected $mInsertId = null;
        protected $mLastResult = null;
        protected $mAffectedRows = null;
        protected $mSubqueryId = 0;
        protected $mScrollableCursor = true;
        protected $mPrepareStatements = true;
        protected $mBinaryColumnCache = null;
        protected $mBitColumnCache = null;
        protected $mIgnoreDupKeyErrors = false;
        protected $mIgnoreErrors = [];

        protected $mPort;

        public function cascadingDeletes() {
                return true;
        }

        public function cleanupTriggers() {
                return false;
        }

        public function strictIPs() {
                return false;
        }

        public function realTimestamps() {
                return false;
        }

        public function implicitGroupby() {
                return false;
        }

        public function implicitOrderby() {
                return false;
        }

        public function functionalIndexes() {
                return true;
        }

        public function unionSupportsOrderAndLimit() {
                return false;
        }

        /**
         * Usually aborts on failure
         * @param string $server
         * @param string $user
         * @param string $password
         * @param string $dbName
         * @throws DBConnectionError
         * @return bool|DatabaseBase|null
         */
        public function open( $server, $user, $password, $dbName ) {
                # Test for driver support, to avoid suppressed fatal error
                if ( !function_exists( 'sqlsrv_connect' ) ) {
                        throw new DBConnectionError(
                                $this,
                                "Microsoft SQL Server Native (sqlsrv) functions missing.
                                You can download the driver from: http://go.microsoft.com/fwlink/?LinkId=123470\n"
                        );
                }

                global $wgDBport, $wgDBWindowsAuthentication;

                # e.g. the class is being loaded
                if ( !strlen( $user ) ) {
                        return null;
                }

                $this->close();
                $this->mServer = $server;
                $this->mPort = $wgDBport;
                $this->mUser = $user;
                $this->mPassword = $password;
                $this->mDBname = $dbName;

                $connectionInfo = [];

                if ( $dbName ) {
                        $connectionInfo['Database'] = $dbName;
                }

                // Decide which auth scenerio to use
                // if we are using Windows auth, don't add credentials to $connectionInfo
                if ( !$wgDBWindowsAuthentication ) {
                        $connectionInfo['UID'] = $user;
                        $connectionInfo['PWD'] = $password;
                }

                MediaWiki\suppressWarnings();
                $this->mConn = sqlsrv_connect( $server, $connectionInfo );
                MediaWiki\restoreWarnings();

                if ( $this->mConn === false ) {
                        throw new DBConnectionError( $this, $this->lastError() );
                }

                $this->mOpened = true;

                return $this->mConn;
        }

        /**
         * Closes a database connection, if it is open
         * Returns success, true if already closed
         * @return bool
         */
        protected function closeConnection() {
                return sqlsrv_close( $this->mConn );
        }

        /**
         * @param bool|MssqlResultWrapper|resource $result
         * @return bool|MssqlResultWrapper
         */
        protected function resultObject( $result ) {
                if ( !$result ) {
                        return false;
                } elseif ( $result instanceof MssqlResultWrapper ) {
                        return $result;
                } elseif ( $result === true ) {
                        // Successful write query
                        return $result;
                } else {
                        return new MssqlResultWrapper( $this, $result );
                }
        }

        /**
         * @param string $sql
         * @return bool|MssqlResult
         * @throws DBUnexpectedError
         */
        protected function doQuery( $sql ) {
                if ( $this->debug() ) {
                        wfDebug( "SQL: [$sql]\n" );
                }
                $this->offset = 0;

                // several extensions seem to think that all databases support limits
                // via LIMIT N after the WHERE clause well, MSSQL uses SELECT TOP N,
                // so to catch any of those extensions we'll do a quick check for a
                // LIMIT clause and pass $sql through $this->LimitToTopN() which parses
                // the limit clause and passes the result to $this->limitResult();
                if ( preg_match( '/\bLIMIT\s*/i', $sql ) ) {
                        // massage LIMIT -> TopN
                        $sql = $this->LimitToTopN( $sql );
                }

                // MSSQL doesn't have EXTRACT(epoch FROM XXX)
                if ( preg_match( '#\bEXTRACT\s*?\(\s*?EPOCH\s+FROM\b#i', $sql, $matches ) ) {
                        // This is same as UNIX_TIMESTAMP, we need to calc # of seconds from 1970
                        $sql = str_replace( $matches[0], "DATEDIFF(s,CONVERT(datetime,'1/1/1970'),", $sql );
                }

                // perform query

                // SQLSRV_CURSOR_STATIC is slower than SQLSRV_CURSOR_CLIENT_BUFFERED (one of the two is
                // needed if we want to be able to seek around the result set), however CLIENT_BUFFERED
                // has a bug in the sqlsrv driver where wchar_t types (such as nvarchar) that are empty
                // strings make php throw a fatal error "Severe error translating Unicode"
                if ( $this->mScrollableCursor ) {
                        $scrollArr = [ 'Scrollable' => SQLSRV_CURSOR_STATIC ];
                } else {
                        $scrollArr = [];
                }

                if ( $this->mPrepareStatements ) {
                        // we do prepare + execute so we can get its field metadata for later usage if desired
                        $stmt = sqlsrv_prepare( $this->mConn, $sql, [], $scrollArr );
                        $success = sqlsrv_execute( $stmt );
                } else {
                        $stmt = sqlsrv_query( $this->mConn, $sql, [], $scrollArr );
                        $success = (bool)$stmt;
                }

                // make a copy so that anything we add below does not get reflected in future queries
                $ignoreErrors = $this->mIgnoreErrors;

                if ( $this->mIgnoreDupKeyErrors ) {
                        // ignore duplicate key errors
                        // this emulates INSERT IGNORE in MySQL
                        $ignoreErrors[] = '2601'; // duplicate key error caused by unique index
                        $ignoreErrors[] = '2627'; // duplicate key error caused by primary key
                        $ignoreErrors[] = '3621'; // generic "the statement has been terminated" error
                }

                if ( $success === false ) {
                        $errors = sqlsrv_errors();
                        $success = true;

                        foreach ( $errors as $err ) {
                                if ( !in_array( $err['code'], $ignoreErrors ) ) {
                                        $success = false;
                                        break;
                                }
                        }

                        if ( $success === false ) {
                                return false;
                        }
                }
                // remember number of rows affected
                $this->mAffectedRows = sqlsrv_rows_affected( $stmt );

                return $stmt;
        }

        public function freeResult( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                sqlsrv_free_stmt( $res );
        }

        /**
         * @param MssqlResultWrapper $res
         * @return stdClass
         */
        public function fetchObject( $res ) {
                // $res is expected to be an instance of MssqlResultWrapper here
                return $res->fetchObject();
        }

        /**
         * @param MssqlResultWrapper $res
         * @return array
         */
        public function fetchRow( $res ) {
                return $res->fetchRow();
        }

        /**
         * @param mixed $res
         * @return int
         */
        public function numRows( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                $ret = sqlsrv_num_rows( $res );

                if ( $ret === false ) {
                        // we cannot get an amount of rows from this cursor type
                        // has_rows returns bool true/false if the result has rows
                        $ret = (int)sqlsrv_has_rows( $res );
                }

                return $ret;
        }

        /**
         * @param mixed $res
         * @return int
         */
        public function numFields( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                return sqlsrv_num_fields( $res );
        }

        /**
         * @param mixed $res
         * @param int $n
         * @return int
         */
        public function fieldName( $res, $n ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                return sqlsrv_field_metadata( $res )[$n]['Name'];
        }

        /**
         * This must be called after nextSequenceVal
         * @return int|null
         */
        public function insertId() {
                return $this->mInsertId;
        }

        /**
         * @param MssqlResultWrapper $res
         * @param int $row
         * @return bool
         */
        public function dataSeek( $res, $row ) {
                return $res->seek( $row );
        }

        /**
         * @return string
         */
        public function lastError() {
                $strRet = '';
                $retErrors = sqlsrv_errors( SQLSRV_ERR_ALL );
                if ( $retErrors != null ) {
                        foreach ( $retErrors as $arrError ) {
                                $strRet .= $this->formatError( $arrError ) . "\n";
                        }
                } else {
                        $strRet = "No errors found";
                }

                return $strRet;
        }

        /**
         * @param array $err
         * @return string
         */
        private function formatError( $err ) {
                return '[SQLSTATE ' . $err['SQLSTATE'] . '][Error Code ' . $err['code'] . ']' . $err['message'];
        }

        /**
         * @return string
         */
        public function lastErrno() {
                $err = sqlsrv_errors( SQLSRV_ERR_ALL );
                if ( $err !== null && isset( $err[0] ) ) {
                        return $err[0]['code'];
                } else {
                        return 0;
                }
        }

        /**
         * @return int
         */
        public function affectedRows() {
                return $this->mAffectedRows;
        }

        /**
         * SELECT wrapper
         *
         * @param mixed $table Array or string, table name(s) (prefix auto-added)
         * @param mixed $vars Array or string, field name(s) to be retrieved
         * @param mixed $conds Array or string, condition(s) for WHERE
         * @param string $fname Calling function name (use __METHOD__) for logs/profiling
         * @param array $options Associative array of options (e.g.
         *   array('GROUP BY' => 'page_title')), see Database::makeSelectOptions
         *   code for list of supported stuff
         * @param array $join_conds Associative array of table join conditions
         *   (optional) (e.g. array( 'page' => array('LEFT JOIN','page_latest=rev_id') )
         * @return mixed Database result resource (feed to Database::fetchObject
         *   or whatever), or false on failure
         * @throws DBQueryError
         * @throws DBUnexpectedError
         * @throws Exception
         */
        public function select( $table, $vars, $conds = '', $fname = __METHOD__,
                $options = [], $join_conds = []
        ) {
                $sql = $this->selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds );
                if ( isset( $options['EXPLAIN'] ) ) {
                        try {
                                $this->mScrollableCursor = false;
                                $this->mPrepareStatements = false;
                                $this->query( "SET SHOWPLAN_ALL ON" );
                                $ret = $this->query( $sql, $fname );
                                $this->query( "SET SHOWPLAN_ALL OFF" );
                        } catch ( DBQueryError $dqe ) {
                                if ( isset( $options['FOR COUNT'] ) ) {
                                        // likely don't have privs for SHOWPLAN, so run a select count instead
                                        $this->query( "SET SHOWPLAN_ALL OFF" );
                                        unset( $options['EXPLAIN'] );
                                        $ret = $this->select(
                                                $table,
                                                'COUNT(*) AS EstimateRows',
                                                $conds,
                                                $fname,
                                                $options,
                                                $join_conds
                                        );
                                } else {
                                        // someone actually wanted the query plan instead of an est row count
                                        // let them know of the error
                                        $this->mScrollableCursor = true;
                                        $this->mPrepareStatements = true;
                                        throw $dqe;
                                }
                        }
                        $this->mScrollableCursor = true;
                        $this->mPrepareStatements = true;
                        return $ret;
                }
                return $this->query( $sql, $fname );
        }

        /**
         * SELECT wrapper
         *
         * @param mixed $table Array or string, table name(s) (prefix auto-added)
         * @param mixed $vars Array or string, field name(s) to be retrieved
         * @param mixed $conds Array or string, condition(s) for WHERE
         * @param string $fname Calling function name (use __METHOD__) for logs/profiling
         * @param array $options Associative array of options (e.g. array('GROUP BY' => 'page_title')),
         *   see Database::makeSelectOptions code for list of supported stuff
         * @param array $join_conds Associative array of table join conditions (optional)
         *    (e.g. array( 'page' => array('LEFT JOIN','page_latest=rev_id') )
         * @return string The SQL text
         */
        public function selectSQLText( $table, $vars, $conds = '', $fname = __METHOD__,
                $options = [], $join_conds = []
        ) {
                if ( isset( $options['EXPLAIN'] ) ) {
                        unset( $options['EXPLAIN'] );
                }

                $sql = parent::selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds );

                // try to rewrite aggregations of bit columns (currently MAX and MIN)
                if ( strpos( $sql, 'MAX(' ) !== false || strpos( $sql, 'MIN(' ) !== false ) {
                        $bitColumns = [];
                        if ( is_array( $table ) ) {
                                foreach ( $table as $t ) {
                                        $bitColumns += $this->getBitColumns( $this->tableName( $t ) );
                                }
                        } else {
                                $bitColumns = $this->getBitColumns( $this->tableName( $table ) );
                        }

                        foreach ( $bitColumns as $col => $info ) {
                                $replace = [
                                        "MAX({$col})" => "MAX(CAST({$col} AS tinyint))",
                                        "MIN({$col})" => "MIN(CAST({$col} AS tinyint))",
                                ];
                                $sql = str_replace( array_keys( $replace ), array_values( $replace ), $sql );
                        }
                }

                return $sql;
        }

        public function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds,
                $fname = __METHOD__
        ) {
                $this->mScrollableCursor = false;
                try {
                        parent::deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds, $fname );
                } catch ( Exception $e ) {
                        $this->mScrollableCursor = true;
                        throw $e;
                }
                $this->mScrollableCursor = true;
        }

        public function delete( $table, $conds, $fname = __METHOD__ ) {
                $this->mScrollableCursor = false;
                try {
                        parent::delete( $table, $conds, $fname );
                } catch ( Exception $e ) {
                        $this->mScrollableCursor = true;
                        throw $e;
                }
                $this->mScrollableCursor = true;
        }

        /**
         * Estimate rows in dataset
         * Returns estimated count, based on SHOWPLAN_ALL output
         * This is not necessarily an accurate estimate, so use sparingly
         * Returns -1 if count cannot be found
         * Takes same arguments as Database::select()
         * @param string $table
         * @param string $vars
         * @param string $conds
         * @param string $fname
         * @param array $options
         * @return int
         */
        public function estimateRowCount( $table, $vars = '*', $conds = '',
                $fname = __METHOD__, $options = []
        ) {
                // http://msdn2.microsoft.com/en-us/library/aa259203.aspx
                $options['EXPLAIN'] = true;
                $options['FOR COUNT'] = true;
                $res = $this->select( $table, $vars, $conds, $fname, $options );

                $rows = -1;
                if ( $res ) {
                        $row = $this->fetchRow( $res );

                        if ( isset( $row['EstimateRows'] ) ) {
                                $rows = (int)$row['EstimateRows'];
                        }
                }

                return $rows;
        }

        /**
         * Returns information about an index
         * If errors are explicitly ignored, returns NULL on failure
         * @param string $table
         * @param string $index
         * @param string $fname
         * @return array|bool|null
         */
        public function indexInfo( $table, $index, $fname = __METHOD__ ) {
                # This does not return the same info as MYSQL would, but that's OK
                # because MediaWiki never uses the returned value except to check for
                # the existance of indexes.
                $sql = "sp_helpindex '" . $this->tableName( $table ) . "'";
                $res = $this->query( $sql, $fname );

                if ( !$res ) {
                        return null;
                }

                $result = [];
                foreach ( $res as $row ) {
                        if ( $row->index_name == $index ) {
                                $row->Non_unique = !stristr( $row->index_description, "unique" );
                                $cols = explode( ", ", $row->index_keys );
                                foreach ( $cols as $col ) {
                                        $row->Column_name = trim( $col );
                                        $result[] = clone $row;
                                }
                        } elseif ( $index == 'PRIMARY' && stristr( $row->index_description, 'PRIMARY' ) ) {
                                $row->Non_unique = 0;
                                $cols = explode( ", ", $row->index_keys );
                                foreach ( $cols as $col ) {
                                        $row->Column_name = trim( $col );
                                        $result[] = clone $row;
                                }
                        }
                }

                return empty( $result ) ? false : $result;
        }

        /**
         * INSERT wrapper, inserts an array into a table
         *
         * $arrToInsert may be a single associative array, or an array of these with numeric keys, for
         * multi-row insert.
         *
         * Usually aborts on failure
         * If errors are explicitly ignored, returns success
         * @param string $table
         * @param array $arrToInsert
         * @param string $fname
         * @param array $options
         * @return bool
         * @throws Exception
         */
        public function insert( $table, $arrToInsert, $fname = __METHOD__, $options = [] ) {
                # No rows to insert, easy just return now
                if ( !count( $arrToInsert ) ) {
                        return true;
                }

                if ( !is_array( $options ) ) {
                        $options = [ $options ];
                }

                $table = $this->tableName( $table );

                if ( !( isset( $arrToInsert[0] ) && is_array( $arrToInsert[0] ) ) ) { // Not multi row
                        $arrToInsert = [ 0 => $arrToInsert ]; // make everything multi row compatible
                }

                // We know the table we're inserting into, get its identity column
                $identity = null;
                // strip matching square brackets and the db/schema from table name
                $tableRawArr = explode( '.', preg_replace( '#\[([^\]]*)\]#', '$1', $table ) );
                $tableRaw = array_pop( $tableRawArr );
                $res = $this->doQuery(
                        "SELECT NAME AS idColumn FROM SYS.IDENTITY_COLUMNS " .
                                "WHERE OBJECT_NAME(OBJECT_ID)='{$tableRaw}'"
                );
                if ( $res && sqlsrv_has_rows( $res ) ) {
                        // There is an identity for this table.
                        $identityArr = sqlsrv_fetch_array( $res, SQLSRV_FETCH_ASSOC );
                        $identity = array_pop( $identityArr );
                }
                sqlsrv_free_stmt( $res );

                // Determine binary/varbinary fields so we can encode data as a hex string like 0xABCDEF
                $binaryColumns = $this->getBinaryColumns( $table );

                // INSERT IGNORE is not supported by SQL Server
                // remove IGNORE from options list and set ignore flag to true
                if ( in_array( 'IGNORE', $options ) ) {
                        $options = array_diff( $options, [ 'IGNORE' ] );
                        $this->mIgnoreDupKeyErrors = true;
                }

                foreach ( $arrToInsert as $a ) {
                        // start out with empty identity column, this is so we can return
                        // it as a result of the insert logic
                        $sqlPre = '';
                        $sqlPost = '';
                        $identityClause = '';

                        // if we have an identity column
                        if ( $identity ) {
                                // iterate through
                                foreach ( $a as $k => $v ) {
                                        if ( $k == $identity ) {
                                                if ( !is_null( $v ) ) {
                                                        // there is a value being passed to us,
                                                        // we need to turn on and off inserted identity
                                                        $sqlPre = "SET IDENTITY_INSERT $table ON;";
                                                        $sqlPost = ";SET IDENTITY_INSERT $table OFF;";
                                                } else {
                                                        // we can't insert NULL into an identity column,
                                                        // so remove the column from the insert.
                                                        unset( $a[$k] );
                                                }
                                        }
                                }

                                // we want to output an identity column as result
                                $identityClause = "OUTPUT INSERTED.$identity ";
                        }

                        $keys = array_keys( $a );

                        // Build the actual query
                        $sql = $sqlPre . 'INSERT ' . implode( ' ', $options ) .
                                " INTO $table (" . implode( ',', $keys ) . ") $identityClause VALUES (";

                        $first = true;
                        foreach ( $a as $key => $value ) {
                                if ( isset( $binaryColumns[$key] ) ) {
                                        $value = new MssqlBlob( $value );
                                }
                                if ( $first ) {
                                        $first = false;
                                } else {
                                        $sql .= ',';
                                }
                                if ( is_null( $value ) ) {
                                        $sql .= 'null';
                                } elseif ( is_array( $value ) || is_object( $value ) ) {
                                        if ( is_object( $value ) && $value instanceof Blob ) {
                                                $sql .= $this->addQuotes( $value );
                                        } else {
                                                $sql .= $this->addQuotes( serialize( $value ) );
                                        }
                                } else {
                                        $sql .= $this->addQuotes( $value );
                                }
                        }
                        $sql .= ')' . $sqlPost;

                        // Run the query
                        $this->mScrollableCursor = false;
                        try {
                                $ret = $this->query( $sql );
                        } catch ( Exception $e ) {
                                $this->mScrollableCursor = true;
                                $this->mIgnoreDupKeyErrors = false;
                                throw $e;
                        }
                        $this->mScrollableCursor = true;

                        if ( !is_null( $identity ) ) {
                                // then we want to get the identity column value we were assigned and save it off
                                $row = $ret->fetchObject();
                                if ( is_object( $row ) ) {
                                        $this->mInsertId = $row->$identity;

                                        // it seems that mAffectedRows is -1 sometimes when OUTPUT INSERTED.identity is used
                                        // if we got an identity back, we know for sure a row was affected, so adjust that here
                                        if ( $this->mAffectedRows == -1 ) {
                                                $this->mAffectedRows = 1;
                                        }
                                }
                        }
                }
                $this->mIgnoreDupKeyErrors = false;
                return $ret;
        }

        /**
         * INSERT SELECT wrapper
         * $varMap must be an associative array of the form array( 'dest1' => 'source1', ...)
         * Source items may be literals rather than field names, but strings should
         * be quoted with Database::addQuotes().
         * @param string $destTable
         * @param array|string $srcTable May be an array of tables.
         * @param array $varMap
         * @param array $conds May be "*" to copy the whole table.
         * @param string $fname
         * @param array $insertOptions
         * @param array $selectOptions
         * @return null|ResultWrapper
         * @throws Exception
         */
        public function insertSelect( $destTable, $srcTable, $varMap, $conds, $fname = __METHOD__,
                $insertOptions = [], $selectOptions = []
        ) {
                $this->mScrollableCursor = false;
                try {
                        $ret = parent::insertSelect(
                                $destTable,
                                $srcTable,
                                $varMap,
                                $conds,
                                $fname,
                                $insertOptions,
                                $selectOptions
                        );
                } catch ( Exception $e ) {
                        $this->mScrollableCursor = true;
                        throw $e;
                }
                $this->mScrollableCursor = true;

                return $ret;
        }

        /**
         * UPDATE wrapper. Takes a condition array and a SET array.
         *
         * @param string $table Name of the table to UPDATE. This will be passed through
         *                DatabaseBase::tableName().
         *
         * @param array $values An array of values to SET. For each array element,
         *                the key gives the field name, and the value gives the data
         *                to set that field to. The data will be quoted by
         *                DatabaseBase::addQuotes().
         *
         * @param array $conds An array of conditions (WHERE). See
         *                DatabaseBase::select() for the details of the format of
         *                condition arrays. Use '*' to update all rows.
         *
         * @param string $fname The function name of the caller (from __METHOD__),
         *                for logging and profiling.
         *
         * @param array $options An array of UPDATE options, can be:
         *                   - IGNORE: Ignore unique key conflicts
         *                   - LOW_PRIORITY: MySQL-specific, see MySQL manual.
         * @return bool
         * @throws DBUnexpectedError
         * @throws Exception
         * @throws MWException
         */
        function update( $table, $values, $conds, $fname = __METHOD__, $options = [] ) {
                $table = $this->tableName( $table );
                $binaryColumns = $this->getBinaryColumns( $table );

                $opts = $this->makeUpdateOptions( $options );
                $sql = "UPDATE $opts $table SET " . $this->makeList( $values, LIST_SET, $binaryColumns );

                if ( $conds !== [] && $conds !== '*' ) {
                        $sql .= " WHERE " . $this->makeList( $conds, LIST_AND, $binaryColumns );
                }

                $this->mScrollableCursor = false;
                try {
                        $ret = $this->query( $sql );
                } catch ( Exception $e ) {
                        $this->mScrollableCursor = true;
                        throw $e;
                }
                $this->mScrollableCursor = true;
                return true;
        }

        /**
         * Makes an encoded list of strings from an array
         * @param array $a Containing the data
         * @param int $mode Constant
         *      - LIST_COMMA:          comma separated, no field names
         *      - LIST_AND:            ANDed WHERE clause (without the WHERE). See
         *        the documentation for $conds in DatabaseBase::select().
         *      - LIST_OR:             ORed WHERE clause (without the WHERE)
         *      - LIST_SET:            comma separated with field names, like a SET clause
         *      - LIST_NAMES:          comma separated field names
         * @param array $binaryColumns Contains a list of column names that are binary types
         *      This is a custom parameter only present for MS SQL.
         *
         * @throws MWException|DBUnexpectedError
         * @return string
         */
        public function makeList( $a, $mode = LIST_COMMA, $binaryColumns = [] ) {
                if ( !is_array( $a ) ) {
                        throw new DBUnexpectedError( $this,
                                'DatabaseBase::makeList called with incorrect parameters' );
                }

                if ( $mode != LIST_NAMES ) {
                        // In MS SQL, values need to be specially encoded when they are
                        // inserted into binary fields. Perform this necessary encoding
                        // for the specified set of columns.
                        foreach ( array_keys( $a ) as $field ) {
                                if ( !isset( $binaryColumns[$field] ) ) {
                                        continue;
                                }

                                if ( is_array( $a[$field] ) ) {
                                        foreach ( $a[$field] as &$v ) {
                                                $v = new MssqlBlob( $v );
                                        }
                                        unset( $v );
                                } else {
                                        $a[$field] = new MssqlBlob( $a[$field] );
                                }
                        }
                }

                return parent::makeList( $a, $mode );
        }

        /**
         * @param string $table
         * @param string $field
         * @return int Returns the size of a text field, or -1 for "unlimited"
         */
        public function textFieldSize( $table, $field ) {
                $table = $this->tableName( $table );
                $sql = "SELECT CHARACTER_MAXIMUM_LENGTH,DATA_TYPE FROM INFORMATION_SCHEMA.Columns
                        WHERE TABLE_NAME = '$table' AND COLUMN_NAME = '$field'";
                $res = $this->query( $sql );
                $row = $this->fetchRow( $res );
                $size = -1;
                if ( strtolower( $row['DATA_TYPE'] ) != 'text' ) {
                        $size = $row['CHARACTER_MAXIMUM_LENGTH'];
                }

                return $size;
        }

        /**
         * Construct a LIMIT query with optional offset
         * This is used for query pages
         *
         * @param string $sql SQL query we will append the limit too
         * @param int $limit The SQL limit
         * @param bool|int $offset The SQL offset (default false)
         * @return array|string
         * @throws DBUnexpectedError
         */
        public function limitResult( $sql, $limit, $offset = false ) {
                if ( $offset === false || $offset == 0 ) {
                        if ( strpos( $sql, "SELECT" ) === false ) {
                                return "TOP {$limit} " . $sql;
                        } else {
                                return preg_replace( '/\bSELECT(\s+DISTINCT)?\b/Dsi',
                                        'SELECT$1 TOP ' . $limit, $sql, 1 );
                        }
                } else {
                        // This one is fun, we need to pull out the select list as well as any ORDER BY clause
                        $select = $orderby = [];
                        $s1 = preg_match( '#SELECT\s+(.+?)\s+FROM#Dis', $sql, $select );
                        $s2 = preg_match( '#(ORDER BY\s+.+?)(\s*FOR XML .*)?$#Dis', $sql, $orderby );
                        $overOrder = $postOrder = '';
                        $first = $offset + 1;
                        $last = $offset + $limit;
                        $sub1 = 'sub_' . $this->mSubqueryId;
                        $sub2 = 'sub_' . ( $this->mSubqueryId + 1 );
                        $this->mSubqueryId += 2;
                        if ( !$s1 ) {
                                // wat
                                throw new DBUnexpectedError( $this, "Attempting to LIMIT a non-SELECT query\n" );
                        }
                        if ( !$s2 ) {
                                // no ORDER BY
                                $overOrder = 'ORDER BY (SELECT 1)';
                        } else {
                                if ( !isset( $orderby[2] ) || !$orderby[2] ) {
                                        // don't need to strip it out if we're using a FOR XML clause
                                        $sql = str_replace( $orderby[1], '', $sql );
                                }
                                $overOrder = $orderby[1];
                                $postOrder = ' ' . $overOrder;
                        }
                        $sql = "SELECT {$select[1]}
                                        FROM (
                                                SELECT ROW_NUMBER() OVER({$overOrder}) AS rowNumber, *
                                                FROM ({$sql}) {$sub1}
                                        ) {$sub2}
                                        WHERE rowNumber BETWEEN {$first} AND {$last}{$postOrder}";

                        return $sql;
                }
        }

        /**
         * If there is a limit clause, parse it, strip it, and pass the remaining
         * SQL through limitResult() with the appropriate parameters. Not the
         * prettiest solution, but better than building a whole new parser. This
         * exists becase there are still too many extensions that don't use dynamic
         * sql generation.
         *
         * @param string $sql
         * @return array|mixed|string
         */
        public function LimitToTopN( $sql ) {
                // Matches: LIMIT {[offset,] row_count | row_count OFFSET offset}
                $pattern = '/\bLIMIT\s+((([0-9]+)\s*,\s*)?([0-9]+)(\s+OFFSET\s+([0-9]+))?)/i';
                if ( preg_match( $pattern, $sql, $matches ) ) {
                        $row_count = $matches[4];
                        $offset = $matches[3] ?: $matches[6] ?: false;

                        // strip the matching LIMIT clause out
                        $sql = str_replace( $matches[0], '', $sql );

                        return $this->limitResult( $sql, $row_count, $offset );
                }

                return $sql;
        }

        /**
         * @return string Wikitext of a link to the server software's web site
         */
        public function getSoftwareLink() {
                return "[{{int:version-db-mssql-url}} MS SQL Server]";
        }

        /**
         * @return string Version information from the database
         */
        public function getServerVersion() {
                $server_info = sqlsrv_server_info( $this->mConn );
                $version = 'Error';
                if ( isset( $server_info['SQLServerVersion'] ) ) {
                        $version = $server_info['SQLServerVersion'];
                }

                return $version;
        }

        /**
         * @param string $table
         * @param string $fname
         * @return bool
         */
        public function tableExists( $table, $fname = __METHOD__ ) {
                list( $db, $schema, $table ) = $this->tableName( $table, 'split' );

                if ( $db !== false ) {
                        // remote database
                        wfDebug( "Attempting to call tableExists on a remote table" );
                        return false;
                }

                if ( $schema === false ) {
                        global $wgDBmwschema;
                        $schema = $wgDBmwschema;
                }

                $res = $this->query( "SELECT 1 FROM INFORMATION_SCHEMA.TABLES
                        WHERE TABLE_TYPE = 'BASE TABLE'
                        AND TABLE_SCHEMA = '$schema' AND TABLE_NAME = '$table'" );

                if ( $res->numRows() ) {
                        return true;
                } else {
                        return false;
                }
        }

        /**
         * Query whether a given column exists in the mediawiki schema
         * @param string $table
         * @param string $field
         * @param string $fname
         * @return bool
         */
        public function fieldExists( $table, $field, $fname = __METHOD__ ) {
                list( $db, $schema, $table ) = $this->tableName( $table, 'split' );

                if ( $db !== false ) {
                        // remote database
                        wfDebug( "Attempting to call fieldExists on a remote table" );
                        return false;
                }

                $res = $this->query( "SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS
                        WHERE TABLE_SCHEMA = '$schema' AND TABLE_NAME = '$table' AND COLUMN_NAME = '$field'" );

                if ( $res->numRows() ) {
                        return true;
                } else {
                        return false;
                }
        }

        public function fieldInfo( $table, $field ) {
                list( $db, $schema, $table ) = $this->tableName( $table, 'split' );

                if ( $db !== false ) {
                        // remote database
                        wfDebug( "Attempting to call fieldInfo on a remote table" );
                        return false;
                }

                $res = $this->query( "SELECT * FROM INFORMATION_SCHEMA.COLUMNS
                        WHERE TABLE_SCHEMA = '$schema' AND TABLE_NAME = '$table' AND COLUMN_NAME = '$field'" );

                $meta = $res->fetchRow();
                if ( $meta ) {
                        return new MssqlField( $meta );
                }

                return false;
        }

        /**
         * Begin a transaction, committing any previously open transaction
         * @param string $fname
         */
        protected function doBegin( $fname = __METHOD__ ) {
                sqlsrv_begin_transaction( $this->mConn );
                $this->mTrxLevel = 1;
        }

        /**
         * End a transaction
         * @param string $fname
         */
        protected function doCommit( $fname = __METHOD__ ) {
                sqlsrv_commit( $this->mConn );
                $this->mTrxLevel = 0;
        }

        /**
         * Rollback a transaction.
         * No-op on non-transactional databases.
         * @param string $fname
         */
        protected function doRollback( $fname = __METHOD__ ) {
                sqlsrv_rollback( $this->mConn );
                $this->mTrxLevel = 0;
        }

        /**
         * Escapes a identifier for use inm SQL.
         * Throws an exception if it is invalid.
         * Reference: http://msdn.microsoft.com/en-us/library/aa224033%28v=SQL.80%29.aspx
         * @param string $identifier
         * @throws MWException
         * @return string
         */
        private function escapeIdentifier( $identifier ) {
                if ( strlen( $identifier ) == 0 ) {
                        throw new MWException( "An identifier must not be empty" );
                }
                if ( strlen( $identifier ) > 128 ) {
                        throw new MWException( "The identifier '$identifier' is too long (max. 128)" );
                }
                if ( ( strpos( $identifier, '[' ) !== false )
                        || ( strpos( $identifier, ']' ) !== false )
                ) {
                        // It may be allowed if you quoted with double quotation marks, but
                        // that would break if QUOTED_IDENTIFIER is OFF
                        throw new MWException( "Square brackets are not allowed in '$identifier'" );
                }

                return "[$identifier]";
        }

        /**
         * @param string $s
         * @return string
         */
        public function strencode( $s ) {
                // Should not be called by us

                return str_replace( "'", "''", $s );
        }

        /**
         * @param string|Blob $s
         * @return string
         */
        public function addQuotes( $s ) {
                if ( $s instanceof MssqlBlob ) {
                        return $s->fetch();
                } elseif ( $s instanceof Blob ) {
                        // this shouldn't really ever be called, but it's here if needed
                        // (and will quite possibly make the SQL error out)
                        $blob = new MssqlBlob( $s->fetch() );
                        return $blob->fetch();
                } else {
                        if ( is_bool( $s ) ) {
                                $s = $s ? 1 : 0;
                        }
                        return parent::addQuotes( $s );
                }
        }

        /**
         * @param string $s
         * @return string
         */
        public function addIdentifierQuotes( $s ) {
                // http://msdn.microsoft.com/en-us/library/aa223962.aspx
                return '[' . $s . ']';
        }

        /**
         * @param string $name
         * @return bool
         */
        public function isQuotedIdentifier( $name ) {
                return strlen( $name ) && $name[0] == '[' && substr( $name, -1, 1 ) == ']';
        }

        /**
         * MS SQL supports more pattern operators than other databases (ex: [,],^)
         *
         * @param string $s
         * @return string
         */
        protected function escapeLikeInternal( $s ) {
                return addcslashes( $s, '\%_[]^' );
        }

        /**
         * MS SQL requires specifying the escape character used in a LIKE query
         * or using Square brackets to surround characters that are to be escaped
         * http://msdn.microsoft.com/en-us/library/ms179859.aspx
         * Here we take the Specify-Escape-Character approach since it's less
         * invasive, renders a query that is closer to other DB's and better at
         * handling square bracket escaping
         *
         * @return string Fully built LIKE statement
         */
        public function buildLike() {
                $params = func_get_args();
                if ( count( $params ) > 0 && is_array( $params[0] ) ) {
                        $params = $params[0];
                }

                return parent::buildLike( $params ) . " ESCAPE '\' ";
        }

        /**
         * @param string $db
         * @return bool
         */
        public function selectDB( $db ) {
                try {
                        $this->mDBname = $db;
                        $this->query( "USE $db" );
                        return true;
                } catch ( Exception $e ) {
                        return false;
                }
        }

        /**
         * @param array $options An associative array of options to be turned into
         *   an SQL query, valid keys are listed in the function.
         * @return array
         */
        public function makeSelectOptions( $options ) {
                $tailOpts = '';
                $startOpts = '';

                $noKeyOptions = [];
                foreach ( $options as $key => $option ) {
                        if ( is_numeric( $key ) ) {
                                $noKeyOptions[$option] = true;
                        }
                }

                $tailOpts .= $this->makeGroupByWithHaving( $options );

                $tailOpts .= $this->makeOrderBy( $options );

                if ( isset( $noKeyOptions['DISTINCT'] ) || isset( $noKeyOptions['DISTINCTROW'] ) ) {
                        $startOpts .= 'DISTINCT';
                }

                if ( isset( $noKeyOptions['FOR XML'] ) ) {
                        // used in group concat field emulation
                        $tailOpts .= " FOR XML PATH('')";
                }

                // we want this to be compatible with the output of parent::makeSelectOptions()
                return [ $startOpts, '', $tailOpts, '' ];
        }

        /**
         * Get the type of the DBMS, as it appears in $wgDBtype.
         * @return string
         */
        public function getType() {
                return 'mssql';
        }

        /**
         * @param array $stringList
         * @return string
         */
        public function buildConcat( $stringList ) {
                return implode( ' + ', $stringList );
        }

        /**
         * Build a GROUP_CONCAT or equivalent statement for a query.
         * MS SQL doesn't have GROUP_CONCAT so we emulate it with other stuff (and boy is it nasty)
         *
         * This is useful for combining a field for several rows into a single string.
         * NULL values will not appear in the output, duplicated values will appear,
         * and the resulting delimiter-separated values have no defined sort order.
         * Code using the results may need to use the PHP unique() or sort() methods.
         *
         * @param string $delim Glue to bind the results together
         * @param string|array $table Table name
         * @param string $field Field name
         * @param string|array $conds Conditions
         * @param string|array $join_conds Join conditions
         * @return string SQL text
         * @since 1.23
         */
        public function buildGroupConcatField( $delim, $table, $field, $conds = '',
                $join_conds = []
        ) {
                $gcsq = 'gcsq_' . $this->mSubqueryId;
                $this->mSubqueryId++;

                $delimLen = strlen( $delim );
                $fld = "{$field} + {$this->addQuotes( $delim )}";
                $sql = "(SELECT LEFT({$field}, LEN({$field}) - {$delimLen}) FROM ("
                        . $this->selectSQLText( $table, $fld, $conds, null, [ 'FOR XML' ], $join_conds )
                        . ") {$gcsq} ({$field}))";

                return $sql;
        }

        /**
         * @return string
         */
        public function getSearchEngine() {
                return "SearchMssql";
        }

        /**
         * Returns an associative array for fields that are of type varbinary, binary, or image
         * $table can be either a raw table name or passed through tableName() first
         * @param string $table
         * @return array
         */
        private function getBinaryColumns( $table ) {
                $tableRawArr = explode( '.', preg_replace( '#\[([^\]]*)\]#', '$1', $table ) );
                $tableRaw = array_pop( $tableRawArr );

                if ( $this->mBinaryColumnCache === null ) {
                        $this->populateColumnCaches();
                }

                return isset( $this->mBinaryColumnCache[$tableRaw] )
                        ? $this->mBinaryColumnCache[$tableRaw]
                        : [];
        }

        /**
         * @param string $table
         * @return array
         */
        private function getBitColumns( $table ) {
                $tableRawArr = explode( '.', preg_replace( '#\[([^\]]*)\]#', '$1', $table ) );
                $tableRaw = array_pop( $tableRawArr );

                if ( $this->mBitColumnCache === null ) {
                        $this->populateColumnCaches();
                }

                return isset( $this->mBitColumnCache[$tableRaw] )
                        ? $this->mBitColumnCache[$tableRaw]
                        : [];
        }

        private function populateColumnCaches() {
                $res = $this->select( 'INFORMATION_SCHEMA.COLUMNS', '*',
                        [
                                'TABLE_CATALOG' => $this->mDBname,
                                'TABLE_SCHEMA' => $this->mSchema,
                                'DATA_TYPE' => [ 'varbinary', 'binary', 'image', 'bit' ]
                        ] );

                $this->mBinaryColumnCache = [];
                $this->mBitColumnCache = [];
                foreach ( $res as $row ) {
                        if ( $row->DATA_TYPE == 'bit' ) {
                                $this->mBitColumnCache[$row->TABLE_NAME][$row->COLUMN_NAME] = $row;
                        } else {
                                $this->mBinaryColumnCache[$row->TABLE_NAME][$row->COLUMN_NAME] = $row;
                        }
                }
        }

        /**
         * @param string $name
         * @param string $format
         * @return string
         */
        function tableName( $name, $format = 'quoted' ) {
                # Replace reserved words with better ones
                switch ( $name ) {
                        case 'user':
                                return $this->realTableName( 'mwuser', $format );
                        default:
                                return $this->realTableName( $name, $format );
                }
        }

        /**
         * call this instead of tableName() in the updater when renaming tables
         * @param string $name
         * @param string $format One of quoted, raw, or split
         * @return string
         */
        function realTableName( $name, $format = 'quoted' ) {
                $table = parent::tableName( $name, $format );
                if ( $format == 'split' ) {
                        // Used internally, we want the schema split off from the table name and returned
                        // as a list with 3 elements (database, schema, table)
                        $table = explode( '.', $table );
                        while ( count( $table ) < 3 ) {
                                array_unshift( $table, false );
                        }
                }
                return $table;
        }

        /**
         * Delete a table
         * @param string $tableName
         * @param string $fName
         * @return bool|ResultWrapper
         * @since 1.18
         */
        public function dropTable( $tableName, $fName = __METHOD__ ) {
                if ( !$this->tableExists( $tableName, $fName ) ) {
                        return false;
                }

                // parent function incorrectly appends CASCADE, which we don't want
                $sql = "DROP TABLE " . $this->tableName( $tableName );

                return $this->query( $sql, $fName );
        }

        /**
         * Called in the installer and updater.
         * Probably doesn't need to be called anywhere else in the codebase.
         * @param bool|null $value
         * @return bool|null
         */
        public function prepareStatements( $value = null ) {
                return wfSetVar( $this->mPrepareStatements, $value );
        }

        /**
         * Called in the installer and updater.
         * Probably doesn't need to be called anywhere else in the codebase.
         * @param bool|null $value
         * @return bool|null
         */
        public function scrollableCursor( $value = null ) {
                return wfSetVar( $this->mScrollableCursor, $value );
        }

        /**
         * Called in the installer and updater.
         * Probably doesn't need to be called anywhere else in the codebase.
         * @param array|null $value
         * @return array|null
         */
        public function ignoreErrors( array $value = null ) {
                return wfSetVar( $this->mIgnoreErrors, $value );
        }
} // end DatabaseMssql class

/**
 * Utility class.
 *
 * @ingroup Database
 */
class MssqlField implements Field {
        private $name, $tableName, $default, $max_length, $nullable, $type;

        function __construct( $info ) {
                $this->name = $info['COLUMN_NAME'];
                $this->tableName = $info['TABLE_NAME'];
                $this->default = $info['COLUMN_DEFAULT'];
                $this->max_length = $info['CHARACTER_MAXIMUM_LENGTH'];
                $this->nullable = !( strtolower( $info['IS_NULLABLE'] ) == 'no' );
                $this->type = $info['DATA_TYPE'];
        }

        function name() {
                return $this->name;
        }

        function tableName() {
                return $this->tableName;
        }

        function defaultValue() {
                return $this->default;
        }

        function maxLength() {
                return $this->max_length;
        }

        function isNullable() {
                return $this->nullable;
        }

        function type() {
                return $this->type;
        }
}

class MssqlBlob extends Blob {
        public function __construct( $data ) {
                if ( $data instanceof MssqlBlob ) {
                        return $data;
                } elseif ( $data instanceof Blob ) {
                        $this->mData = $data->fetch();
                } elseif ( is_array( $data ) && is_object( $data ) ) {
                        $this->mData = serialize( $data );
                } else {
                        $this->mData = $data;
                }
        }

        /**
         * Returns an unquoted hex representation of a binary string
         * for insertion into varbinary-type fields
         * @return string
         */
        public function fetch() {
                if ( $this->mData === null ) {
                        return 'null';
                }

                $ret = '0x';
                $dataLength = strlen( $this->mData );
                for ( $i = 0; $i < $dataLength; $i++ ) {
                        $ret .= bin2hex( pack( 'C', ord( $this->mData[$i] ) ) );
                }

                return $ret;
        }
}

class MssqlResultWrapper extends ResultWrapper {
        private $mSeekTo = null;

        /**
         * @return stdClass|bool
         */
        public function fetchObject() {
                $res = $this->result;

                if ( $this->mSeekTo !== null ) {
                        $result = sqlsrv_fetch_object( $res, 'stdClass', [],
                                SQLSRV_SCROLL_ABSOLUTE, $this->mSeekTo );
                        $this->mSeekTo = null;
                } else {
                        $result = sqlsrv_fetch_object( $res );
                }

                // MediaWiki expects us to return boolean false when there are no more rows instead of null
                if ( $result === null ) {
                        return false;
                }

                return $result;
        }

        /**
         * @return array|bool
         */
        public function fetchRow() {
                $res = $this->result;

                if ( $this->mSeekTo !== null ) {
                        $result = sqlsrv_fetch_array( $res, SQLSRV_FETCH_BOTH,
                                SQLSRV_SCROLL_ABSOLUTE, $this->mSeekTo );
                        $this->mSeekTo = null;
                } else {
                        $result = sqlsrv_fetch_array( $res );
                }

                // MediaWiki expects us to return boolean false when there are no more rows instead of null
                if ( $result === null ) {
                        return false;
                }

                return $result;
        }

        /**
         * @param int $row
         * @return bool
         */
        public function seek( $row ) {
                $res = $this->result;

                // check bounds
                $numRows = $this->db->numRows( $res );
                $row = intval( $row );

                if ( $numRows === 0 ) {
                        return false;
                } elseif ( $row < 0 || $row > $numRows - 1 ) {
                        return false;
                }

                // Unlike MySQL, the seek actually happens on the next access
                $this->mSeekTo = $row;
                return true;
        }
}