public function drop_key(xmldb_table $xmldb_table, xmldb_key $xmldb_key) {
        if ($xmldb_key->getType() == XMLDB_KEY_PRIMARY) { // Prevent PRIMARY to be dropped (only in drop table, being serious  :-P)
            throw new ddl_exception('ddlunknownerror', null, 'Primary Keys can be deleted at table drop time only');
        }

        if (!$sqlarr = $this->generator->getDropKeySQL($xmldb_table, $xmldb_key)) {
            return; //Empty array = nothing to do = no error
        }

        $this->execute_sql_arr($sqlarr, array($xmldb_table->getName()));
    }