Mysql子查询返回多于1行

Question

SELECT * FROM wp_posts WHERE ID IN 
(
(SELECT courses  FROM wp_category WHERE CatID =401) OR 
(SELECT  meta_value FROM wp_postmeta WHERE  post_id IN (SELECT courses FROM wp_category WHERE CatID =401) AND meta_key ='post_id' )
) 
AND 
ID IN (SELECT post_id FROM wp_locations_courses WHERE location_id = 1120)

我在使用IN子查询时遇到上述查询的问题给了我错误Subquery returns more than 1 row为什么在我使用IN子句时会发生

Answer 1

        (SELECT courses  FROM wp_category WHERE CatID =401) 
        OR 
        (SELECT  meta_value FROM wp_postmeta WHERE  post_id IN (SELECT courses FROM wp_category WHERE CatID =401) AND meta_key ='post_id' )

这是一个条件，但您需要n值。

这应该有效：

(
    ID IN 
        (
            (SELECT courses  FROM wp_category WHERE CatID =401) 
        )
    OR
    ID IN 
        (
            (SELECT  meta_value FROM wp_postmeta WHERE  post_id IN 
                (SELECT courses FROM wp_category WHERE CatID =401) AND meta_key ='post_id' )
        )
)

还要注意 MySQL 的子查询。在你的情况下是一个子子查询。

看看这里：https : //stackoverflow.com/questions/12356784/mysql-dependent-sub-query-with-not-in-in-the-where-clause-is-very-slow