MySQL-查询速度非常慢

Question

I have statements like this that are timing out: 我有这样的语句正在超时：

SELECT COUNT(*) FROM A WHERE A.value1 IN (
  SELECT A.value1 FROM A WHERE A.value2 = 0
)

Table A has 13,000,000+ rows in it, and because of some reasons, I can't use indexes. 表A中有13,000,000+行，由于某些原因，我不能使用索引。

So how to speed it up without use indexes? 那么如何在不使用索引的情况下加快速度呢？ I'm using MySQL 5.6. 我正在使用MySQL 5.6。

Any help please. 请帮忙。

Answer 1

I would first try using exists . 我首先尝试使用exists 。 This often optimizes better: 这通常可以更好地进行优化：

SELECT COUNT(*)
FROM A 
WHERE EXISTS (SELECT 1
              FROM A A2
              WHERE A2.value2 = 0 AND A2.value1 = A.value1
             );

The optimal index for this is A(value2, value1) . 最佳索引是A(value2, value1) 。

You could also use two levels of aggregation: 您还可以使用两种聚合级别：

select sum(cnt)
from (select value1, count(*) as cnt
      from a
      group by value1
      having sum(value2 = 0) > 0
     ) a;