SQL Server中表之间的参照完整性

Question

I have 2 tables, Members and Enrollments . Both tables can be joined using primary key Member ID .

I need to write a query which returns all the members in the Members table which don't have a corresponding row in the Enrollments table and vice versa.

This is what I have so far:

IF OBJECT_ID('tempdb..#memberswithoutenrollments') IS NOT NULL
    DROP TABLE #memberswithoutenrollments 

SELECT m.* 
INTO #memberswithoutenrollments 
FROM ABC_Members m 
LEFT OUTER JOIN ABC_MemEnrollment e ON m.MemberID = MemberID

Answer 1

FULL JOIN is a simple method for comparing lists between two tables:

SELECT COALESCE(e.MemberID, m.MemberID),
       (CASE WHEN e.MemberID IS NULL THEN 'No Enrollments' ELSE 'No Member' END)
FROM ABC_Members m FULL JOIN
     ABC_MemEnrollment e
     ON m.MemberID = e.MemberID
WHERE e.MemberID IS NULL OR m.MemberID IS NULL;

But if you have proper foreign key relationships, then you should never have enrollments without members.

Answer 2

You can use NOT IN to your benefit here.

WITH
    -- Create a list of all of the matches
    in_table AS
        (
            SELECT
                Member_ID
            FROM
                Enrollments
            WHERE
                Members.MemberID = Enrollments.Member_ID
        ),

    result_table AS
        (
            SELECT
                *

            FROM
                Members

            -- Grab only the values from members that DO NOT APPEAR in in_table
            WHERE
                MemberID NOT IN (SELECT DISTINCT FROM in_table)
        )

-- Grab all results
SELECT * FROM result_table