/**
* Get SQL code suitable to create a temporary table of the given name, used to store ids.
* MySQL can do that simply by creating new temporary tables. PostgreSQL first checks if such
* a table exists, so the code is ready to reuse existing tables if the code was modified to
* keep them after query answering. Also, PostgreSQL tables will use a RULE to achieve built-in
* duplicate elimination. The latter is done using INSERT IGNORE in MySQL.
*
* @param string $tableName
*
* @return string
*/
private function getSQLCodeFor($tableName)
{
// PostgreSQL: no memory tables, use RULE to emulate INSERT IGNORE
if ($this->connection->isType('postgres')) {
// Remove any double quotes from the name
$tableName = str_replace('"', '', $tableName);
return "DO \$\$BEGIN " . " IF EXISTS(SELECT NULL FROM pg_tables WHERE tablename='{$tableName}' AND schemaname = ANY (current_schemas(true))) " . " THEN DELETE FROM {$tableName}; " . " ELSE " . " CREATE TEMPORARY TABLE {$tableName} (id INTEGER PRIMARY KEY); " . " CREATE RULE {$tableName}_ignore AS ON INSERT TO {$tableName} WHERE (EXISTS (SELECT 1 FROM {$tableName} " . "\t WHERE ({$tableName}.id = new.id))) DO INSTEAD NOTHING; " . " END IF; " . "END\$\$";
}
// MySQL_ just a temporary table, use INSERT IGNORE later
return "CREATE TEMPORARY TABLE " . $tableName . "( id INT UNSIGNED KEY ) ENGINE=MEMORY";
}