Question

嗨，我有一个UNION beetween到表格如下：

SELECT GetStudentClassmates.AvatarFileName  as AvatarFileName,
       GetStudentClassmates.UserName        as UserName,
       GetStudentClassmates.RoleId          as RoleId
FROM GetStudentClassmates
WHERE GetStudentClassmates.StudentId = @studentId

UNION

SELECT GetStudentTeachers.AvatarFileName    as AvatarFileName,
       GetStudentTeachers.UserName          as UserName,
       GetStudentTeachers.RoleId            as RoleId
FROM GetStudentTeachers

现在我需要将UNION的结果加入到其他表中，并在最终结果中添加另一列。

这是我正在使用的JOIN代码

LEFT OUTER JOIN Sync_StudentAssignments as StudentAssignments 
  ON @studentId = StudentAssignments.StudentID 
  AND StudentAssignments.Deletion_Date IS NULL
LEFT OUTER JOIN Sync_StudentAssignmentInstances as StudentAssignmentInstances 
  ON StudentAssignments.StudentAssignmentID = StudentAssignmentInstances.StudentAssignmentID 
  AND StudentAssignmentInstances.Deletion_Date IS NULL

我的问题是我不知道在哪里添加选择代码，我觉得这看起来像这样：

SELECT StudentAssignmentInstances.ModuleInstanceId

我的决赛桌应该包含以下列：

AvatarFileName,
UserName,
RoleId,
ModuleInstanceId

我怎样才能做到这一点？

Answer 1

将UNION位括在括号中并将其用作内联表，然后正常加入：

-----------------------------------------------------------
-- choose the exact columns you need here using the aliases
-----------------------------------------------------------
select x.*, ssa.*, ssai.* from
(
   select ....
   union
   select ....
) as x
inner join Sync_StudentAssignments ssa on ...
inner join Sync_StudentAssignmentInstances ssai on ....

Answer 2

在SQL Server中如果要加入某个联合，可以使用子选择表单或CTE。在这里，我将使用CTE，因为它在TSQL代码中添加了一些顺序......

;WITH Participants AS (
  SELECT GetStudentClassmates.AvatarFileName  as AvatarFileName,
         GetStudentClassmates.UserName        as UserName,
         GetStudentClassmates.RoleId          as RoleId
  FROM GetStudentClassmates
  WHERE GetStudentClassmates.StudentId = @studentId

  UNION ALL

  SELECT GetStudentTeachers.AvatarFileName    as AvatarFileName,
         GetStudentTeachers.UserName          as UserName,
         GetStudentTeachers.RoleId            as RoleId
  FROM GetStudentTeachers)
SELECT
FROM 
  Participants p
  JOIN WhateverYouWant wyw
    ON wyw.{column1} = p.{column1}
    AND wyw.{column2} = p.{column2}
    ...

此处WhateverYouWant可能是您的Sync_StudentAssignments JOIN Sync_StudentAssignmentInstances。但是，你已经加入了使用变量和const，这将产生笛卡尔积，我相信这不是你的意图。

修改

现在我更仔细地看待你的情况，我相信你必须做到以下几点：

;WITH Participants AS ( SELECT GetStudentClassmates.AvatarFileName, GetStudentClassmates.UserName, GetStudentClassmates.RoleId, GetStudentClassmates.StudentId FROM GetStudentClassmates --WHERE GetStudentClassmates.StudentId = @studentId --uncomment previous line only if you need just one student in your recordset UNION ALL SELECT GetStudentTeachers.AvatarFileName, GetStudentTeachers.UserName, GetStudentTeachers.RoleId, GetStudentClassmates.TeacherId AS StudentId -- just guessing column name FROM GetStudentTeachers --previous select means you need all of the teachers, no matter which student ) SELECT p.AvatarFileName, p.UserName, p.RoleId, StudentAssignmentInstances.ModuleInstanceId FROM Participants p LEFT JOIN Sync_StudentAssignments as StudentAssignments ON p.StudentId = StudentAssignments.StudentID AND StudentAssignments.Deletion_Date IS NULL LEFT JOIN Sync_StudentAssignmentInstances as StudentAssignmentInstances ON StudentAssignments.StudentAssignmentID = StudentAssignmentInstances.StudentAssignmentID AND StudentAssignmentInstances.Deletion_Date IS NULL

Answer 3

SELECT tbl.AvartarFileName, 
       tbl.UserName, 
       tbl.RoleId, 
       StudentAssignmentInstances.ModuleInstanceId
FROM
(
    SELECT GetStudentClassmates.AvatarFileName  as AvatarFileName,
           GetStudentClassmates.UserName        as UserName,
           GetStudentClassmates.RoleId          as RoleId
      FROM GetStudentClassmates
     WHERE GetStudentClassmates.StudentId = @studentId

     UNION

    SELECT GetStudentTeachers.AvatarFileName    as AvatarFileName,
           GetStudentTeachers.UserName          as UserName,
           GetStudentTeachers.RoleId            as RoleId
           FROM GetStudentTeachers
) AS tbl
LEFT OUTER JOIN Sync_StudentAssignments as StudentAssignments 
  ON @studentId = StudentAssignments.StudentID 
  AND StudentAssignments.Deletion_Date IS NULL
LEFT OUTER JOIN Sync_StudentAssignmentInstances as StudentAssignmentInstances 
  ON StudentAssignments.StudentAssignmentID = StudentAssignmentInstances.StudentAssignmentID 
  AND StudentAssignmentInstances.Deletion_Date IS NULL

在UNION之后创建SELECT和JOIN

3 个答案: