显示一个表中的所有记录，并显示另一个表中的匹配记录

Question

嗨，我在下面的表格中记录了活动和分数

Activites
|A_ID   |Site        | ActivityValue| ActivityName
 ---------------------------------------------------
|1      | site1      | 7             | ActivityName1
|2      | site1      | 6             | ActivityName2
|2      | site1      | 6             | ActivityName3
|2      | site1      | 6             | ActivityName4



pointsTable
|UserID |RemainderPoints  | Active         | ActivityName |
------------------------------------------------------
|1      | 10              | TRUE           | ActivityName1| 
|2      | 5               | TRUE           | ActivityName2| 
|2      | 5               | TRUE           | ActivityName3| 
|2      | 5               | TRUE           | ActivityName3|

我需要从活动中返回所有记录

SELECT  ActivityName FROM activity WHERE `Site`='Site1'

退货

ActivityName1
ActivityName2
ActivityName3
ActivityName4

然后我需要基于来自点表的用户ID对用户点求和

SELECT UserID, ActivityName, Active,  SUM( RemainderPoints) 
FROM pointstable
WHERE UserID =2
AND Active =  'TRUE'  GROUP BY ActivityName

退货

|UserID |RemainderPoints   | Active         | ActivityName |
-------------------------------------------------------------
|2      | 5                | TRUE           | ActivityName2| 
|2      | 10               | TRUE           | ActivityName3|

一切都很好，但我需要将它们放在一起给用户，即

ActivityName1  = 0
ActivityName2  = 5
ActivityName3  =10
ActivityName4  = 0

有指针吗？

Answer 1

使用外部联接：

select 
    a.activityName, 
    coalesce(sum(pt.remainderPoints), 0) points
from 
    activities a left outer join pointsTable pt on 
        pt.activityName = a.activityName and pt.UserID = 2
group by a.activityName

或子查询：

select
    activities.ActivityName,
    coalesce(
        (select sum(RemainderPoints) from pointsTable where pointsTable.UserId = 2 and pointsTable.ActivityName = activities.ActivityName)
    , 0) points
from
    activities