Mysql查詢（order by）很慢

Question

當我從另一個表使用 ORDER BY 時，它的工作速度非常慢。 如何進行查詢

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

您的查詢格式不正確。 試試下面的查詢：

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

您可能還需要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)