wp-includes/class-wpdb.php:3479Checks if the query is accessing a collation considered safe on the current version of MySQL.
$querystringbool protected function check_safe_collation( $query ) { if ( $this->checking_collation ) { return true; } // We don't need to check the collation for queries that don't read data. $query = ltrim( $query, "\r\n\t (" ); if ( preg_match( '/^(?:SHOW|DESCRIBE|DESC|EXPLAIN|CREATE)\s/i', $query ) ) { return true; } // All-ASCII queries don't need extra checking. if ( $this->check_ascii( $query ) ) { return true; } $table = $this->get_table_from_query( $query ); if ( ! $table ) { return false; } $this->checking_collation = true; $collation = $this->get_table_charset( $table ); $this->checking_collation = false; // Tables with no collation, or latin1 only, don't need extra checking. if ( false === $collation || 'latin1' === $collation ) { return true; } $table = strtolower( $table ); if ( empty( $this->col_meta[ $table ] ) ) { return false; } // If any of the columns don't have one of these collations, it needs more confidence checking. $safe_collations = array( 'utf8_bin', 'utf8_general_ci', 'utf8mb3_bin', 'utf8mb3_general_ci', 'utf8mb4_bin', 'utf8mb4_general_ci', ); foreach ( $this->col_meta[ $table ] as $col ) { if ( empty( $col->Collation ) ) { continue; } if ( ! in_array( $col->Collation, $safe_collations, true ) ) { return false; } } return true; }Introduced in 4.2.0. Unchanged from 6.7.7 through 7.1.0.
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src/wp-includes/class-wpdb.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.