Mysql查询（order by）很慢

Question

当我从另一个表使用 ORDER BY 时，它的工作速度非常慢。 如何进行查询

SELECT u.*, (SELECT COUNT(id) FROM operations o WHERE o.userId=u.userId and o.status=1) as countOperations FROM users u ORDER BY countOperations

Answer 1

您的查询格式不正确。 试试下面的查询：

select col1, col2, ..., coln, count(id) countOperations, SUM(o.sumRUB) sumRUB
from users u
inner join operations o 
  on o.userId=u.userId and o.status=1
group by col1, col2, ..., coln
ORDER BY countOperations

您可能还需要operations(userId, status)索引operations(userId, status)和可能（您可能不需要） users(col1, col2, ..., coln)索引users(col1, col2, ..., coln)