在两个表中选择一对多的关系加入

Question

a16s            
id  pic     
1   1.jpg       
2   2.jpg       
3   3.jpg       
4   4.jpg       

a16s_like           
id  p_id u_id   approve
1   1       2   0
2   1       1   1
3   1       5   1
4   1       6   1
5   1       7   0
6   2       2   0
7   2       3   0
8   2       1   1
9   4       4   0
10  4       3   1
11  4       2   1


$sql="SELECT A.id, A.pic

(select count(*) from a16s_like B where B.p_id = A.id) AS Ashow, 
(select count(*) from a16s_like B where B.p_id = A.id and B.approve='0') AS Nshow,
(select count(*) from a16s_like B where B.p_id = A.id and B.approve='1') AS Yshow
FROM a16s A  ORDER BY id DESC";

我用了3次approvic colume，有什么方法可以说服seach吗？ 我的目的是

当 u_id=2 执行 select 时，我想得到

id pic    Ashowocunt  approve_0_count  approve_1_count     u_id2_approve   
1  1.jpg   5          2                3                   0
2  2.jpg   3          2                1                   0
3  3.jpg   0          0                0                   null
4. 4.jpg   3          0                3                   0

u_id=3

id pic    Ashowocunt  approve_0_count  approve_1_count     u_id3_approve   
1  1.jpg   0          0                0                   null
2  2.jpg   0          1                0                   0
3  3.jpg   0          0                0                   null
4. 4.jpg   1          0                1                   1    

需要显示变量 u_id 的所有 a.id，就像 u_id=2 或 u_id=3（有 null）

Answer 1

你可以试试这个。

使用CASE express 和FULL OUTER JOIN

但是Mysql不支持FULL OUTER JOIN，所以需要使用LEFT JOIN和Right JOIN来实现。

SELECT 
    A.id, 
    A.PIC, 
    SUM(CASE WHEN  B.approve IS NULL THEN 0 ELSE 1 END) AS Ashowocunt,
    SUM(CASE WHEN  B.approve=0 THEN 1 ELSE 0 END) AS Nshow,
    SUM(CASE WHEN  B.approve=1 THEN 1 ELSE 0 END) AS Yshow
FROM  
(
  SELECT A.id ID
  FROM  a16s AS A
  LEFT JOIN a16s_like  AS B ON A.ID = B.p_id 
  UNION 
  SELECT B.p_id ID
  FROM  a16s AS A
  RIGHT JOIN a16s_like  AS B ON A.ID = B.p_id 
) AS T
LEFT JOIN a16s AS A ON A.ID = T.ID
LEFT JOIN a16s_like  AS B ON T.ID = B.p_id 
GROUP BY A.id,A.PIC 

编辑

您可以在a16s_like上使用子查询

SELECT 
    A.id, 
    A.PIC, 
    SUM(CASE WHEN  B.approve IS NULL THEN 0 ELSE 1 END) AS Ashowocunt,
    SUM(CASE WHEN  B.approve=0 THEN 1 ELSE 0 END) AS Nshow,
    SUM(CASE WHEN  B.approve=1 THEN 1 ELSE 0 END) AS Yshow
FROM  
(
  SELECT A.id ID
  FROM  a16s AS A
  LEFT JOIN a16s_like  AS B ON A.ID = B.p_id 
  UNION 
  SELECT B.p_id ID
  FROM  a16s AS A
  RIGHT JOIN a16s_like  AS B ON A.ID = B.p_id 
) AS T
LEFT JOIN a16s AS A ON A.ID = T.ID
LEFT JOIN 
(
SELECT * 
FROM  a16s_like
WHERE u_id=2
)  AS B ON T.ID = B.p_id 
GROUP BY A.id,A.PIC 

您可以通过另一种方式在CASE express 上设置B.approve=1 AND B.u_id=2

SUM(CASE WHEN  B.approve=1 AND B.u_id=2 THEN 1 ELSE 0 END) AS Yshow 

SQLFiddle