Question

我正在使用NOT IN在一个大约有10万行的表上运行下面的查询，性能非常糟糕。还有另一种方法可以达到同样的效果吗？

SELECT c.Id, c.Name, c.address, c.town,
c.county, c.postcode, FROM contractor AS c
inner join Order w
on w.Id = c.Id WHERE (c.valid = 1) and c.Id not in
(select w.Id from Order w) ORDER BY c.Name ASC

由于

Answer 1

您似乎有一个冗余的内部联接Order 我相信以下查询会产生相同的结果，并可能提高性能。

SELECT  c.Id
        , c.Name
        , c.address
        , c.town
        , c.county
        , c.postcode
FROM    contractor AS c 
        left outer join Order w on w.Id = c.Id 
WHERE   (c.valid = 1) 
        and w.Id IS NULL
ORDER BY 
        c.Name ASC

Answer 2

我个人无法看到您的代码的进一步改进，除了您可能想要为您的字段添加索引。一般规则是为您在WHERE子句中使用的列添加索引。

MySql NOT IN性能问题

2 个答案: