如何正确查询 SQL 中的复杂连接语句的结果？

Question

新手到高级SQL！

我正在尝试编写一个查询，该查询 returns 来自该查询的结果列的 COUNT(*) 和 SUM：

DECLARE @Id INT = 1000;

SELECT 
    *,
    CASE
        WHEN Id1 >= 6 THEN 1
        ELSE 0
    END AS Tier1,
    CASE
        WHEN Id1 >= 4 THEN 1
        ELSE 0
    END AS Tier2,
    CASE
        WHEN Id1 >= 2 THEN 1
        ELSE 0
    END AS Tier3
    FROM (
        SELECT
            Org.OrgID,
            App.AppID,
            App.FirstName,
            App.LastName,
            MAX(AppSubmitU_Level.Id1) AS Id1
        FROM Org
        INNER JOIN AppEmployment
            ON AppEmployment.OrgID = Org.OrgID
        INNER JOIN App
            ON App.AppID = AppEmployment.AppID
        INNER JOIN AppSubmit
            ON App.AppID = AppSubmit.AppID
        INNER JOIN AppSubmitU_Level
            ON AppSubmit.LevelID = AppSubmitU_Level.Id1
        INNER JOIN AppEmpU_VerifyStatus
            ON AppEmpU_VerifyStatus.VerifyStatusID = AppEmployment.VerifyStatusID
        WHERE AppSubmitU_Level.SubmitTypeID = 1 -- Career
        AND AppEmpU_VerifyStatus.StatusIsVerified = 1
        AND AppSubmit.[ExpireDate] IS NOT NULL
        AND AppSubmit.[ExpireDate] > GETDATE()
        AND Org.OrgID = @Id
        GROUP BY
            Org.OrgID,
            App.AppID,
            App.FirstName,
            App.LastName
    ) employees

我尝试通过将 @Id 移到原始查询之外，并在顶部添加 SELECT(*)、SUM 和 SUM 来做到这一点，如下所示：

DECLARE @OrgID INT = 1000;

SELECT COUNT(*), SUM(employees.Tier1), SUM(employees.Tier2), SUM(employees.Tier3) 
FROM
    (SELECT *,
        ...
    ) AS employees
);

但是，当我运行查询时，出现错误：

The multi-part identifier employees.Tier1 could not be bound

我的 SUM 语句中的其他标识符出现相同的错误。

我假设这与以下事实有关：Tier1、Tier2 和 Tier3 列由我的 FROM() 中的内部联接查询返回，并且不是由现有表设置的值我在查询但我不知道如何重写它以正确初始化。

在此先感谢您的帮助！

Answer 1

这是一个作用域问题：employees 仅在子查询中定义，在外部作用域中不可用。您基本上想为外部查询设置别名：

DECLARE @OrgID INT = 1000;
SELECT COUNT(*), SUM(employees.Tier1) TotalTier1, SUM(employees.Tier2) TotalTier2, SUM(employees.Tier3) TotalTier3
FROM (
    SELECT *,
    ...
    ) AS employees
) AS employees;
--^ here

请注意，我向外部查询添加了列别名，这是 SQL 中的一个好习惯。

如果您为外部查询使用另一个别名，可能会更容易理解发生了什么：

SELECT COUNT(*), SUM(e.Tier1), SUM(e.Tier2), SUM(e.Tier3) 
FROM (
    SELECT *,
    ...
    ) AS employees
) AS e;

请注意，您实际上不需要在外部查询中限定列名，因为列名无论如何都是明确的。

最后：您实际上不需要子查询。您可以将查询写成：

SELECT 
    SUM(CASE WHEN Id1 >= 6 THEN 1 ELSE 0 END) AS TotalTier1,
    SUM(CASE WHEN Id1 >= 4 THEN 1 ELSE 0 END) AS TotalTier2,
    SUM(CASE WHEN Id1 >= 2 THEN 1 ELSE 0 END) AS TotalTier3
FROM (
    SELECT
        Org.OrgID,
        App.AppID,
        App.FirstName,
        App.LastName,
        MAX(AppSubmitU_Level.Id1) AS Id1
    FROM Org
    INNER JOIN AppEmployment
        ON AppEmployment.OrgID = Org.OrgID
    INNER JOIN App
        ON App.AppID = AppEmployment.AppID
    INNER JOIN AppSubmit
        ON App.AppID = AppSubmit.AppID
    INNER JOIN AppSubmitU_Level
        ON AppSubmit.LevelID = AppSubmitU_Level.Id1
    INNER JOIN AppEmpU_VerifyStatus
        ON AppEmpU_VerifyStatus.VerifyStatusID = AppEmployment.VerifyStatusID
    WHERE AppSubmitU_Level.SubmitTypeID = 1 -- Career
    AND AppEmpU_VerifyStatus.StatusIsVerified = 1
    AND AppSubmit.[ExpireDate] IS NOT NULL
    AND AppSubmit.[ExpireDate] > GETDATE()
    AND Org.OrgID = @Id
    GROUP BY
        Org.OrgID,
        App.AppID,
        App.FirstName,
        App.LastName
) employees

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