php - MySQL FULL JOIN 一个表，并在同一个查询中 LEFT JOIN 另一个表？

Question

我想在这个查询中链接三个表。

该脚本是一个出席登记簿，因此它会为每个用户记录每个 session 的出席标记。

用到的三个表:

“团队”:

id | fullname | position         | class | hidden
1  | Team     | --               | black | 1
2  | Dan S    | Team Manager     | green | 0
3  | Harry P  | Graphic Engineer | blue  | 0

“注册”:

id | mid | uid | mark
1  | 1   | 2   | /
2  | 1   | 3   | I
3  | 2   | 1   | /
4  | 2   | 3   | /

“ session ”:

id | maintask            | starttime  | endtime
1  | Organise Year Ahead | 1330007400 | 1330012800
2  | Gather Ideas        | 1330612200 | 1330617600
3  | TODO                | 1331217000 | 1331222400

有一个数据样本。我想做的是:

从寄存器中选择所有结果，按用户分组，并按 session 开始时间排序。但是，如果注册表中没有标记，我希望它显示“-”(如果需要可以通过 php 完成)所以预期结果如下:

fullname | mark | mid
Dan S    | /    | 1
Dan S    | /    | 2
Dan S    | -    | 3
Harry P  | I    | 1
Harry P  | /    | 2
Harry P  | -    | 3

目前我的 SQL 查询是这样的:

SELECT u.fullname,u.id,r.mark,r.mid FROM team u FULL JOIN register r ON r.uid=u.id LEFT JOIN meetings m ON r.mid=m.id GROUP BY u.id ORDER BY m.starttime ASC

我从 MySQL 返回一个错误:

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 'FULL JOIN register r ON r.uid=u.id LEFT JOIN meetings m ON r.mid=m.`id' at line 1

但是，我看不出它有什么问题 :S

请有人帮忙，指出正确的方向或给我一个可能的解决方案。非常感谢

丹

回答:有效的查询:

   SELECT     
       u.fullname,    u.id as uid,    
       if(r.uid = u.id, r.mark, '-') as mark,    
       if(r.uid = u.id, r.mid, '-') as mid,    
       r.mid,    m.starttime 
   FROM     
       team u 
         CROSS JOIN     
       register r ON u.id = r.uid
         LEFT OUTER JOIN     
       meetings m ON r.mid = m.id  
   WHERE    
       u.hidden = 0 
   GROUP BY     
       u.id, r.mid 
   ORDER BY     
       m.starttime, u.id ASC

Answer 1

MySQL 不支持

Full outer join。至少到5.6版本，可以查看MySQL Join doc . cross join 可能是一种解决方法:

已编辑

SELECT 
   UxM.fullname,
   r.mark,
   UxM.mid,
   UxM.starttime
FROM 
   ( select u.id as uid, m.id as mid, u.fullname, m.starttime
     from
     team  u
      CROSS JOIN   
     meetings ) UxM
   left join
   register r
      on UxM.uid = r.uid and UxM.mid = r.mid
ORDER BY 
   UxM.starttime ASC

如果这能解决您的问题，请告诉我。

---

一个简化:

SELECT     
    u.fullname,
    u.id AS uid,    
    COALESCE(r.mark, '-') AS mark,    
    COALESCE(r.mid, '-') AS mid,    
    m.id,
    m.starttime 
FROM     
    team u 
      CROSS JOIN     
    meetings m 
      LEFT JOIN     
    register r
        ON   r.mid = m.id  
        AND  r.id = u.uid
WHERE    
    u.hidden = 0 
GROUP BY     
    m.id, u.id 
ORDER BY     
    m.starttime, u.id