运行缓慢的简单Mysql查询

Question

我有一个非常简单的MySQL查询，但是运行起来非常慢。我有两个表corporate_main_member和corporate_main_corporate_membership，并且我正在运行以下查询：

SELECT m.gender FROM corporate_main_member m, corporate_main_corporate_membership cm where m.id = cm.FK_member_ID and cm.FK_corporation_id = 6

当我不包含第二个条件(cm.FK_corporation_id = 6)时，查询运行OK...

Answer 1

在查询中使用JOIN关键字，并在FK_corporation_id上创建索引。

SELECT m.gender 
FROM   corporate_main_member m 
       INNER JOIN corporate_main_corporate_membership cm 
               ON m.id = cm.fk_member_id 
WHERE  cm.fk_corporation_id = 6 

Answer 2

这是上述查询的更有效形式。

SELECT 
m.gender 
FROM corporate_main_member m,
 corporate_main_corporate_membership cm on(m.id = cm.FK_member_ID)
where cm.FK_corporation_id = 6

而您可以在corporate_main_corporate_membership上创建索引。

Answer 3

SELECT
  m.gender
FROM corporate_main_member AS m
  LEFT JOIN corporate_main_corporate_membership AS cm
ON m.id = cm.FK_member_ID
    AND cm.FK_corporation_id = 6