Mutually Exclusive Queries

Question How would you role an IF...ELSE that produces mutually exclusive results into a query that produces the same results? Use Case As the principal (currently logged in user)

Solution 1:

Use a union with the "if" condition added to each where clause:

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)

Solution 2:

 SELECT du.userId as UserId,
            'Department' as UserType // remove this line unnecessary
      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

      UNION ALL

      -- Get all user IDs in the organization.
      SELECT userId as UserId,
             'Organization' as UserType // remove this line unnecessary
      FROM dbo.OrganizationsUsers
      WHERE organizationId = @organizationId