Question

我有一个带连接表的select语句，我试图选择连接表的第一行。

例如，dbo.Projects有许多dbo.Buffers。

我的查询是：

SELECT PM.PROJECTID, PM.PROJECTNAME, BU.PERCENTPENWREALIGNED
FROM dbo.PROJECTMGRVIEW AS PM
JOIN dbo.S2M_BUFFER AS BU ON BU.PROJECTID = ( SELECT DISTINCT MIN(TASKUNIQUEID) FROM dbo.S2M_BUFFER WHERE PROJECTID = PM.PROJECTID )
WHERE PM.PROJECT_TYPE = 8 AND PM.CATEGORY = 'Engineering' ANd PM.PROJECTID = 244;

我的结果集有很多行：

PROJECTID | PROJECTNAME | PERCENTPENWREALIGNED
244       | PROJECT A   | 100
244       | PROJECT A   | 0
244       | PROJECT A   | 0
244       | PROJECT A   | 0
244       | PROJECT A   | 0
244       | PROJECT A   | 0
244       | PROJECT A   | 0

显然在这种情况下，我只需要第一行。

Answer 1

你的联接没有任何意义，你不能使用子查询来做，但我猜你想要这样的东西：

SELECT PM.PROJECTID, PM.PROJECTNAME, BU.PERCENTPENWREALIGNED
FROM dbo.PROJECTMGRVIEW AS PM
CROSS APPLY (
  select top 1 PERCENTPENWREALIGNED
  from dbo.S2M_BUFFER BU 
  where BU.PROJECTID = PM.PROJECTID
  order by TASKUNIQUEID ASC
) BU
WHERE PM.PROJECT_TYPE = 8 AND PM.CATEGORY = 'Engineering' AND PM.PROJECTID = 244;

这将使用PROJECTMGRVIEW

将S2M_BUFFER中具有最小TASKUNIQUEID的行加入

Answer 2

我同意您的加入声明因PROJECTID和TASKUNIQUEID之间的循环引用而存在缺陷。

我认为这可能是你想要做的更多：

SELECT PM.PROJECTID, PM.PROJECTNAME, BU.PERCENTPENWREALIGNED
FROM dbo.PROJECTMGRVIEW AS PM
JOIN dbo.S2M_BUFFER AS BU ON BU.TASKUNIQUEID = 
( SELECT DISTINCT MIN(TASKUNIQUEID) FROM dbo.S2M_BUFFER WHERE PROJECTID = PM.PROJECTID )
WHERE PM.PROJECT_TYPE = 8 AND PM.CATEGORY = 'Engineering' ANd PM.PROJECTID = 244;

未选择SQL Min值

2 个答案: