Question

我目前正在MS SQL Server 2012中进行复杂的T-SQL查询。我基本上检索了一个基本的项目列表，包含ProjectId以及StaffVersionId（工作人员可能会在整个项目中进行更改，虽然我希望情况不是这样：P）。

CREATE TABLE #BasicProjects
    (
        ProjectId INT
        , StaffVersionId INT
    )

接下来，我需要加入ProjectData Table以获取项目的标题，并加入Employee Table以获取Employee的FullName。

SELECT [P].ProjectId
    , [PD].Label AS Title
    , [E].Lastname + '' '' + Firstname AS Manager
    , [E].Lastname + '' '' + Firstname AS Contact
    FROM #BasicProjects [P]
    INNER JOIN [MySchema].[ProjectData] [PD] ON [PD].ProjectDataId = [P].ProjectDataId 
    INNER JOIN [MySchema].[Staff] [Y] ON [Y].StaffVersionId = [P].StaffVersionId AND [Y].StaffTypeId = 3 // Manager
    INNER JOIN [MySchema].[Staff] [X] ON [X].StaffVersionId = [P].StaffVersionId AND [X].StaffTypeId = 2 // Contact
    INNER JOIN [dbo].[Employee] [E] ON [E].EmployeeId = [Y].EmployeeId
    INNER JOIN [dbo].[Employee] [E] ON [E].EmployeeId = [X].EmployeeId

查询有点难，因为我有2种员工3 =经理，2 =联系。

当我运行查询时，我收到此错误：

在FROM子句中多次指定相关名称“E”。

你知道如何解决这个错误吗？或者也许有人建议如何改进这个查询？

非常感谢！

Answer 1

每个联接需要不同的别名（就像您对Staff所做的那样）

SELECT [P].ProjectId
    , [PD].Label AS Title
    , [YE].Lastname + ' ' + YE.Firstname AS Manager
    , [XE].Lastname + ' ' + XE.Firstname AS Contact
    FROM #BasicProjects [P]
    INNER JOIN [MySchema].[ProjectData] [PD] ON [PD].ProjectDataId = [P].ProjectDataId 
    INNER JOIN [MySchema].[Staff] [Y] ON [Y].StaffVersionId = [P].StaffVersionId AND [Y].StaffTypeId = 3 // Manager
    INNER JOIN [MySchema].[Staff] [X] ON [X].StaffVersionId = [P].StaffVersionId AND [X].StaffTypeId = 2 // Contact
    INNER JOIN [dbo].[Employee] [YE] ON [YE].EmployeeId = [Y].EmployeeId
    INNER JOIN [dbo].[Employee] [XE] ON [XE].EmployeeId = [X].EmployeeId

T-SQL多个连接在1个表

1 个答案: