Question

where meetingID = [[WHERE IT MATCHES]] (select meetingID from meeting where categoryID = '1')

我不太清楚要把这两个加在一起怎么样？

Answer 1

如果某个类别可以包含多个meetingID，则最好使用IN而不是=，这样就不会产生错误，

SELECT ...
FROM ....
where meetingID IN (select meetingID 
                    from meeting 
                     where categoryID = '1')

另一种方式是JOIN他们，例如

SELECT DISTINCT a.*
FROM   tableName a
       INNER JOIN meeting b
           ON a.meetingID = b.meetingID 
WHERE  b.categoryID  = '1'

Answer 2

使用加入会提高效果。

SELECT ... 
FROM tablea a 
INNER JOIN meeting m ON a.meetingID = m.meetingID AND m.categoryID = '1'

或

SELECT ... 
FROM tablea a 
INNER JOIN (SELECT meetingID 
            FROM meeting 
            WHERE categoryID = '1'
          ) b ON a.meetingID = b.meetingID;

点击此链接MySQL Optimizing Subqueries

MYSQL从其他表执行切线查询？

2 个答案: