用外连接连接 3 个查询答案

【问题标题】：joining 3 queries with outer join用外连接连接 3 个查询
【发布时间】：2010-07-30 14:03:38
【问题描述】：

我创建了一个表 tblOperationLog 并编写了触发器来填充它，因为用户在我的主表中删除、更新或插入一行。就是删除和插入：

CREATE TRIGGER FILL_TABLE  
ON Person FOR INSERT, DELETE
AS  

  INSERT INTO tblOperationLog  
 SELECT  SYSTEM_USER, 
         'user has inserted a row with ID = ' + Convert(nvarchar, inserted.id), 
          'Insert', CURRENT_TIMESTAMP, getdate()
  FROM inserted 


  INSERT INTO tblOperationLog  
 SELECT  SYSTEM_USER, 
         'user has deleted a row with ID = ' + Convert(nvarchar, deleted.id), 
          'Insert', CURRENT_TIMESTAMP, getdate() 
  FROM deleted

现在我想编写一个程序来显示每个用户每天执行的操作的平均值。我想在单独的列中获得每个操作（删除、插入和更新）的平均值。为了实现这个目标，我编写了以下查询：

select A.Users , avg(A.[Number Of Inserts])as 'Number Of Inserts' from
(select  Users,[Time],COUNT(*) as 'Number Of Inserts' from tblOperationLog where Opertion='Insert' group by Users, [Date]) A  group by Users

go
select B.Users , avg(B.[Number Of Updates])as 'Number Of Updates' from
(select  Users,[Date],COUNT(*) as 'Number Of Updates' from tblOperationLog where Operation='Update' group by Users, [Date]) B  group by Users

go

select C.Users , avg(C.[Number Of Deletes])as 'Number Of Deletes' from
(select  Users,[Date],COUNT(*) as 'Number Of Deletes' from tblOperationLog where Operation='Delete' group by Users, [Date]) C  group by Users

Go

通过上述程序，我将每个操作显示在一个单独的表中。但是我希望将它们全部放在一张表中，并且我希望对于没有删除或...操作 0 的用户平均拥有。你能帮我加入他们吗？我想我必须使用完全外连接。但是每次我的最终查询都有错误。我使用 SQL Server。

【问题讨论】：

标签： sql-server join

【解决方案1】：

查看“UNION”SQL 运算符

【讨论】：

你能告诉我如何加入他们吗，我使用它但我无法得到结果
联合不起作用，因为查询中的列名不同

【解决方案2】：

这是一个可能有效的查询。

WITH OpLogCTE AS (
    SELECT Users, Date, Operation, AVG(COUNT(*)) OVER (PARTITION BY Users, Date, Operation) AS OpCount
    FROM tblOperationLog
    GROUP BY Users, Date, Operation
    )

SELECT Users, Date,
    SUM(CASE Operation WHEN 'Insert' THEN OpCount ELSE 0 END) AS InsertCount,
    SUM(CASE Operation WHEN 'Update' THEN OpCount ELSE 0 END) AS UpdateCount,
    SUM(CASE Operation WHEN 'Delete' THEN OpCount ELSE 0 END) AS DeleteCount
FROM OpLogCTE
GROUP BY Users, Date
ORDER BY Users, Date

顶部是公用表表达式 (CTE)。它包含一个查询，用于获取每个用户、日期和操作的平均值。

下半部分获取 CTE 的结果并将数据分组，以便为每个用户和日期获取一行。

【讨论】：

【解决方案3】：

这是你需要的吗？（你是不是要计算每个用户每天的平均操作次数）

SELECT * 
INTO #tblOperationLog
FROM (
SELECT 'Alice' AS Users, CAST('2010-07-29' AS DATE) AS [DATE],
'Delete' AS OPERATION UNION ALL
SELECT 'Bob' AS Users, CAST('2010-07-30' AS DATE) AS [DATE],
'Insert' AS OPERATION UNION ALL
SELECT 'Bob' AS Users, CAST('2010-07-30' AS DATE) AS [DATE],
'Insert' AS OPERATION
) DemoData


DECLARE @DateCount float 
SELECT @DateCount= COUNT(DISTINCT [DATE]) FROM #tblOperationLog

SELECT Users,
COUNT(CASE WHEN OPERATION = 'Delete' THEN 1 END)/@DateCount AS DelAverage,
COUNT(CASE WHEN OPERATION = 'Insert' THEN 1 END)/@DateCount AS UpdateAverage,
COUNT(CASE WHEN OPERATION = 'Update' THEN 1 END)/@DateCount AS InsertAverage
FROM #tblOperationLog
GROUP BY Users

输出

Users DelAverage             UpdateAverage          InsertAverage
----- ---------------------- ---------------------- ----------------------
Alice 0.5                    0                      0
Bob   0                      1                      0

【讨论】：