UPDATE列使用SELECT子查询的结果

Question

This query returns an error : "Subquery returns more than one row":

UPDATE forums as f 
SET f.f_last_pid = (SELECT pid FROM  posts ORDER BY  ptime DESC )

I know that i need to use ANY before the subquery but that won't get the proper result I want. I want to update every row in my forums table based on the result shown from the subquery.

Answer 1

UPDATE forums as f 
SET f.f_last_pid = 
    (SELECT pid FROM posts ORDER BY ptime DESC LIMIT 1 )

But (without really knowing your schema), you're not joining these tables on anything. Every last_pid in forums would be updated by the last post in posts

Answer 2

UPDATE forums as f
SET f.f_last_pid = (SELECT pid FROM posts ORDER BY ptime DESC LIMIT 1)