Question

我编写了以下查询，该查询提取当前用户部门的子部门中的所有用户。当前用户来自客户端应用程序，但我出于测试原因在SQL中对其进行了Decalred。

DECLARE @UserID INT = 72

SELECT * 
FROM users
WHERE Department_Id IN ( 
                        SELECT DISTINCT Id    /*, idp*/
                        FROM departments
                        WHERE idp IN (
                                        SELECT Department_Id 
                                        FROM users 
                                        WHERE Id = @UserID
                                        )
                        )

OR Department_Id IN (
                        SELECT DISTINCT idp
                        FROM departments
                        WHERE idp IN (
                                        SELECT Department_Id 
                                        FROM users 
                                        WHERE Id = @UserID
                                        )
                        )

我想从部门中选择 ID 和 idp 来进行简短查询，但是当我使用这种方式时，它会返回给我SQL错误：

当子查询未与EXISTS一起引入时，只能在选择列表中指定一个表达式。

这是因为我的列表应该只包含一列，而不是2列。

请以任何方式建议我减少此查询，尤其是第二部分（在 OR 之后），这是第一部分的复制粘贴（在 OR 之前）

谢谢。

Answer 1

尝试使用EXISTS这样的

SELECT * 
FROM   users u
WHERE  EXISTS(  SELECT *
                FROM   departments
                WHERE  idp IN (SELECT Department_Id FROM users WHERE Id = @UserID)
                       AND (id = u.Department_Id
                           OR idp = u.Department_Id)    )

Answer 2

一些想法......

嵌套的IN子查询不太友好。
使用IN

我会使用GROUP BY来处理1：很多关系，但是当你的答案是使用另一种结构时，我会尽量接近你所拥有的......

DECLARE @UserID INT = 72

SELECT
  *
FROM
  users AS associates
WHERE
  EXISTS (
    SELECT 
      *
    FROM
      users
    INNER JOIN      
      departments
        ON departments.idp = users.Department_Id
    WHERE
      users.id = @user_id
      AND (   departments.id  = associates.department_id
           OR departments.idp = associates.department_id)
  )

如果您确实使用了GROUP BY方法，则可以避免所有子查询和相关子查询......

DECLARE @UserID INT = 72

SELECT
  associates.id
FROM
  users
INNER JOIN      
  departments
    ON departments.idp = users.Department_Id
INNER JOIN
  users AS associates
    ON associates.department_id = departments.id
    OR associates.department_id = departments.idp
WHERE
  users.id = @user_id
GROUP BY
  associates.id

如果您需要associates中的任何其他字段，只需将它们添加到SELECT 和 GROUP BY。

Answer 3

SELECT * 
FROM users
WHERE Department_Id IN ( 
                    SELECT myId FROM 
                     ( SELECT Id AS myId
                       FROM departments
                       UNION ALL
                       SELECT idp AS myId
                       FROM departments
                     ) A 
                    WHERE A.myId IN (
                                    SELECT Department_Id 
                                    FROM users 
                                    WHERE Id = @UserID
                                    )
                    )

SQL - 如何优化查询

3 个答案: