이 구문 사용의 핵심은 쿼리 연산시 혼란을 피하기 위해
NULL값 비교시 a = NULL 또는 a <> NULL 사용을 가능한 배제하고,
IS NULL 또는 IS NOT NULL 을 사용하자는데 있다.
-- Create table t1 and insert values.
CREATE TABLE t1 (a INT NULL)
INSERT INTO t1 values (NULL)
INSERT INTO t1 values (0)
INSERT INTO t1 values (1)
GO
-- Print message and perform SELECT statements.
PRINT 'Testing default setting'
DECLARE @varname int
SELECT @varname = NULL
SELECT *
FROM t1
WHERE a = @varname
SELECT *
FROM t1
WHERE a <> @varname
SELECT *
FROM t1
WHERE a IS NULL
GO
-- SET ANSI_NULLS to ON and test.
PRINT 'Testing ANSI_NULLS ON'
SET ANSI_NULLS ON
GO
DECLARE @varname int
SELECT @varname = NULL
SELECT *
FROM t1
WHERE a = @varname
SELECT *
FROM t1
WHERE a <> @varname
SELECT *
FROM t1
WHERE a IS NULL
GO
-- SET ANSI_NULLS to OFF and test.
PRINT 'Testing SET ANSI_NULLS OFF'
SET ANSI_NULLS OFF
GO
DECLARE @varname int
SELECT @varname = NULL
SELECT *
FROM t1
WHERE a = @varname
SELECT *
FROM t1
WHERE a <> @varname
SELECT *
FROM t1
WHERE a IS NULL
GO
-- Drop table t1.
DROP TABLE t1