MySQL ORDER BY问题

Question

如何添加一个由users_friends.date_created来管理两个select查询的订单。

这是我的MySQL代码。

(SELECT A.user_id, A.friend_id, B.username, B.avatar 
FROM users_friends AS A 
INNER JOIN users AS B 
ON A.friend_id = B.user_id 
AND A.user_id = 3 
AND A.friendship_status = 1) 
UNION 
(SELECT A.friend_id, A.user_id, B.username, B.avatar 
FROM users_friends AS A 
INNER JOIN users AS B 
ON B.user_id = A.user_id 
AND A.friend_id = 3 
AND A.friendship_status = 1) 
LIMIT 10 

Answer 1

您可以通过添加外选择与订单和包裹工会作为派生表

SELECT user_id, friend_id, username, avatar FROM (
(SELECT A.user_id, A.friend_id, B.username, B.avatar 
FROM users_friends AS A 
INNER JOIN users AS B 
ON A.friend_id = B.user_id 
AND A.user_id = 3 
AND A.friendship_status = 1) 
UNION 
(SELECT A.friend_id, A.user_id, B.username, B.avatar 
FROM users_friends AS A 
INNER JOIN users AS B 
ON B.user_id = A.user_id 
AND A.friend_id = 3 
AND A.friendship_status = 1) 
LIMIT 10 
) C 
ORDER BY avatar 

Answer 2

如果选择DATE_CREATED列在查询中也是允许的话，可以责令联盟结果是 -

(SELECT A.user_id, A.friend_id, B.username, B.avatar, A.date_created as createdDate 
FROM users_friends AS A 
INNER JOIN users AS B 
ON A.friend_id = B.user_id 
AND A.user_id = 3 
AND A.friendship_status = 1) 
UNION 
(SELECT A.friend_id, A.user_id, B.username, B.avatar, A.date_created as createdDate 
FROM users_friends AS A 
INNER JOIN users AS B 
ON B.user_id = A.user_id 
AND A.friend_id = 3 
AND A.friendship_status = 1) 
order by createdDate LIMIT 10