查询执行得很慢？

Question

我有一个表，其中有四个列ID，MID，SID和Amt，我准备查询以使用级别对amt的总和进行计数。

赞：

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')))

但是花了很多时间，我想一直到第15级

Answer 1

EXPLAIN [your query here]

这将帮助您了解查询和表的当前状态。

在表上添加索引将有助于提高查询性能。