MySql 基于字段值连接表

Question

是否可以做这样的事情:

SELECT 
  p.*, u.*
FROM
  posts AS p 
  IF(p.status = 1) 
  LEFT JOIN users AS u 
    ON u.id = p.user_id 
    ELSE 
  LEFT JOIN pusers AS u 
    ON u.id = p.user_id 
WHERE p.id = 10 ;

根据帖子状态为真/假加入 users/pusers 表

Answer 1

不，但你可以这样做:

SELECT p.*,
       (case when p.status = 1 then u.col1 else pu.col1 end) as col1
FROM posts p LEFT JOIN
     users u 
     ON u.id = p.user_id and p.status = 1 LEFT JOIN
     pusers AS pu 
     ON pu.id = p.user_id and p.status <> 1
WHERE p.id = 10 ;

换句话说，您可以连接两个表并根据条件使用表中的值。