互斥查询

Question

您如何将产生互斥结果的 IF...ELSE 分配到产生相同结果的查询中？

Use Case

作为主体（当前登录的用户），我可以获得组织中的用户列表。如果我被分配到任何部门，那么用户列表是分配到相同部门的较小的集合。

Example

DECLARE @organizationId int = 421;
DECLARE @userId int = 1138;

IF EXISTS (SELECT * FROM dbo.DepartmentsUsers WHERE organizationId = @organizationId AND userId = @userId)
  -- Get user IDs in the same department(s) as the principal.
  SELECT du.userId
  FROM dbo.DepartmentsUsers AS du
  JOIN (
        -- Get department IDs assigned to the principal.
        SELECT departmentId
        FROM dbo.DepartmentsUsers
        WHERE organizationId = @organizationId
          AND userId = @userId) AS j
    ON du.departmentId = j.departmentId
  WHERE du.organizationId = @organizationId
ELSE
  -- Get all user IDs in the organization.
  SELECT userId
  FROM dbo.OrganizationsUsers
  WHERE organizationId = @organizationId

使用联合并将“if”条件添加到每个 where 子句：

SELECT du.userId
FROM dbo.DepartmentsUsers AS du
JOIN (  SELECT departmentId
        FROM dbo.DepartmentsUsers
        WHERE organizationId = @organizationId
          AND userId = @userId) AS j
    ON du.departmentId = j.departmentId
WHERE du.organizationId = @organizationId
AND EXISTS (SELECT * FROM dbo.DepartmentsUsers WHERE organizationId = @organizationId AND userId = @userId)
UNION
SELECT userId
FROM dbo.OrganizationsUsers
WHERE organizationId = @organizationId
AND NOT EXISTS (SELECT * FROM dbo.DepartmentsUsers WHERE organizationId = @organizationId AND userId = @userId)