$mergeSql = 'MERGE INTO ' . $this->db->quoteTableName($table) . ' '
            . 'USING (' . (!empty($placeholders) ? 'VALUES (' . implode(', ', $placeholders) . ')' : ltrim($values, ' ')) . ') AS "EXCLUDED" (' . implode(', ', $insertNames) . ') '
            . "ON ($on)";