mysql - MySQL 中 UNION 附近的语法错误？

Question

SELECT * 
FROM Activity AA
WHERE AA.act_id IN 
((SELECT A.act_id 
  FROM Activity A 
  WHERE A.user_id = 'lhfcws')
 UNION
 (SELECT J.act_id 
  FROM Joinin J 
  WHERE J.user_id = 'lhfcws'))
ORDER BY AA.act_time 

ERROR MESSAGE: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UNION (SELECT J.act_id FROM Joinin J WHERE J.user_id = 'lhfcws')) ORDE' at line 7

事件(act_id, user_id, act_name)
Joinin(act_id, user_id)

Answer 1

错误的原因是 select 语句周围的括号。你应该写成:

SELECT * 
FROM Activity AA
WHERE AA.act_id IN 
(SELECT A.act_id 
  FROM Activity A 
  WHERE A.user_id = 'lhfcws'
 UNION
 SELECT J.act_id 
  FROM Joinin J 
  WHERE J.user_id = 'lhfcws')
ORDER BY AA.act_time

但请仔细阅读@Raphaël Althaus 改进查询的想法。