Question

好的，所以我设法为用户75选择了朋友ID，我怎么能弄清楚如何从用户表中为朋友ID选择users.firstname，users.lastname 我不能删除IF声明，因为我的朋友之一会被淹没，因为这会破坏其他查询。

SELECT IF(friends.sender = 75, friends.recipient, friends.sender) users.firstname, users.lastname AS user_id
FROM friends
JOIN users 
ON (users.id = friends.sender)
WHERE friends.sender = 75
    OR friends.recipient = 75

Answer 1

在子查询中选择好友ID，然后将其加入users。

SELECT u.firstname, u.lastname
FROM users as u
JOIN (SELECT DISTINCT IF(friends.sender = 75, friends.recipient, friends.sender) AS friend
      FROM friends
      WHERE 75 in (sender, recipient)) AS f
ON f.friend = u.id

使用friends表从users表中选择firstnames和lastnames

1 个答案: