Mysql sub query returns more than 1 row
(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' )
This is a condition, but you need n
values.
This should work:
(
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' )
)
)
Also take care about subqueries with MySQL. In your case a sub- subquery.
Take a look here: https://stackoverflow.com/questions/12356784/mysql-dependent-sub-query-with-not-in-in-the-where-clause-is-very-slow