sqlisnotnull与isnull用法

is null 判断为空的内容

4>
5> CREATE TABLE titleauthor(
6> au_id varchar(20),
7> title_id varchar(20),
8> au_ord tinyint NULL,
9> royaltyper int NULL
10> )
11> GO
1>
2> insert titleauthor values(null, '2', 1, 60)
3> insert titleauthor values('2', '3', 1, 100)
4> insert titleauthor values('3', '4', 1, 100)
5> insert titleauthor values('4', '5', 1, 100)
6> insert titleauthor values('5', '6', 1, 100)
7> insert titleauthor values('6', '7', 2, 40)
8> insert titleauthor values('7', '8', 1, 100)
9> insert titleauthor values('8', '9', 1, 100)
10> GO

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)
1>
2> * from titleauthor where au_id is null;
3> GO
au_id title_id au_ord royaltyper
-------------------- -------------------- ------ -----------
NULL 2 1 60

(1 rows affected)
1> select * from titleauthor where au_id = null;
2> GO
au_id title_id au_ord royaltyper
-------------------- -------------------- ------ -----------

(0 rows affected)