加入在MySQL

Question

三個表我有三個表

表1

student_id | id | status 
-------------------------------- 

10 | 100 | 1 
11 | 100 | 1 
12 | 100 | 1 
13 | 100 | 1 
10 | 200 | 1 
11 | 200 | 1 
12 | 200 | 1 
13 | 200 | 1 

表2

​​

表3

date | id 
------------------------  
2013-12-28 | 100 
2013-12-30 | 200 

我需要所有一個空值學生日期2013-12-29

例如：

sid |日期|狀態|日期|狀態 ------------------------------------------------ -------

10 | 2013-12-28 | 1  | 2013-12-28 | cd 
11 | 2013-12-28 | 1  | 2013-12-28 | cd 
12 | 2013-12-28 | 1  | 2013-12-28 | cd 
13 | 2013-12-28 | 1  | 2013-12-28 | cd 
10 | null  | null | 2013-12-29 | wd 
11 | null  | null | 2013-12-29 | wd 
12 | null  | null | 2013-12-29 | wd 
13 | null  | null | 2013-12-29 | wd 
10 | 2013-12-30 | 1  | 2013-12-30 | cd 
11 | 2013-12-30 | 1  | 2013-12-30 | cd 
12 | 2013-12-30 | 1  | 2013-12-30 | cd 
13 | 2013-12-30 | 1  | 2013-12-30 | cd 

我試着用 Join two tables in mysql?

，我用下面的查詢

SELECT distinct x.student_id, table1.status, x.date bdate, table2.status bstatus 
FROM 
    (SELECT DISTINCT table1.student_id, table2.date 
    FROM table1 
      CROSS JOIN table2) x 
      LEFT JOIN table1 ON x.sid=table1.sid 
      left join table3 on table1.id=table3.id and x.date=table3.date 
      LEFT JOIN table2 ON x.date=table2.date ORDER BY bdate, student_id 

，但我did'nt得到第三列狀態空值。

Answer 1

SELECT DISTINCT student_id,t3.date,IF(t3.date IS NULL, NULL,t1.status) as status,t2.date as date2,t2.status as status2 
FROM table2 t2 
LEFT JOIN table3 t3 USING(date) 
JOIN table1 t1 ON (t1.id = t3.id OR t3.id IS NULL) 
ORDER BY date2,student_id 

sqlFiddle