查詢執行速度很慢？

Question

我有一個表，其中有四列 ID、MID、SID 和 Amt，我准備查詢以使用 level 計算 amt 的總和。

喜歡：

SELECT Sum(amt) as level1 FROM adm where sid='MT00001';

SELECT Sum(amt) as level2 FROM adm where sid in (SELECT mid FROM adm where sid='MT00001');

SELECT Sum(amt) as level3 FROM adm where sid in (SELECT mid FROM adm where sid in (SELECT mid FROM adm where sid='MT00001'));

SELECT Sum(amt) as level4 FROM adm where sid in (SELECT mid FROM adm where sid in (SELECT mid FROM adm where sid in (SELECT mid FROM adm where sid='MT00001')))

但是花了很多時間，我想要這個直到第 15 級

Answer 1

EXPLAIN [your query here]

這將幫助您了解查詢和表的當前狀態。

在表上添加索引將有助於提高查詢性能。