not in 和 not exists

CREATE TABLE #t1 ( c1 INT, c2 INT );
CREATE TABLE #t2 ( c1 INT, c2 INT );

INSERT  INTO #t1 VALUES  ( 1, 2 );
INSERT  INTO #t1 VALUES  ( 1, 3 );

INSERT  INTO #t2 VALUES  ( 1, 2 );
INSERT  INTO #t2 VALUES  ( 1, NULL );

SELECT  *
FROM    #t1
WHERE   c2 NOT IN ( SELECT  c2  FROM #t2 );
---->执行结果：无

SELECT  *
FROM    #t1
WHERE   NOT EXISTS ( SELECT 1 FROM #t2 WHERE  #t2.c2 = #t1.c2 );
--->执行结果：1　　3