Question

我有3个表格如下：

acc_prop

id | pid | uid
1  | 10  | 1
2  | 11  | 1
3  | 12  | 1

卡

id | pid
1  | 10
2  | 11
3  | 12

价

cid | rate
1   | 100
2   | 99
3   | 130

我想创建一个返回pid的查询，一个具有相同uid的uid的计数，以及该pid的速率。

预期结果

pid  | uid_count | rate
10   | 3         | 100
11   | 3         | 99
12   | 3         | 130

我的查询看起来像这样

SELECT 
    cal.pid,
    count(ap3.uid) as uid_count,
    price.rate 
 FROM
    price 
 JOIN 
    cal on cal.id = price.cid
 JOIN
    acc_prop ap using(pid)
 JOIN
    acc_prop ap2 on ap2.uid = ap.uid
 JOIN
    acc_prop ap3 on ap3.uid = ap2.uid
 group by  ap3.pid;

但它返回

错误的计数
错误的pid列表
错误率

实际结果

pid  | uid_count | rate
10   | 9         | 100
10   | 9         | 100

Answer 1

我认为这里不需要cal，你试过这个吗？

SELECT 
    acc_prop.pid, (SELECT COUNT(*) FROM acc_prop WHERE uid = uid) AS uid_count, price.rate
FROM 
acc_prop 
INNER JOIN price
ON acc_prop.id = price.cid

Answer 2

我认为你所追求的是这个，即预先计算acc_prop中作为派生表的用户数量，然后你可以将其加入到查询的其余部分：

SELECT 
    cal.pid,
    UserCount.Cnt,
    price.rate 
 FROM
    price 
    JOIN cal on cal.id = price.cid
    JOIN acc_prop ap using(pid)
 JOIN
 (
   SELECT uid, COUNT(*) AS Cnt
   FROM acc_prop
   GROUP BY uid
) UserCount
ON ap.uid = UserCount.uid;

SqlFiddle here

MySQL如何在保持唯一文件的同时计算多个条目

2 个答案: