sql 如何查询 空值的字段？

Answer 1

sql查询空值的字段写法：SELECT
A.字段
FROM
student
A
WHERE
A.字段
LIKE'%
%'
（student为表名）
查询类似空值的写法:
1、查询名称有退格键：select
*
from
t_bd_item_info
where
charindex(char(8),item_name)
>
0
go
2、查询名称有制表符tab：select
*
from
t_bd_item_info
where
charindex(char(9),item_name)
>
0
go
3、查询名称有换行：select
*
from
t_bd_item_info
where
charindex(char(10),item_name)
>
0
go
4、查询名称有回车：select
*
from
t_bd_item_info
where
charindex(char(13),item_name)
>
0
go
5、查询名称的空格（前空格、后空格、所有空格）：select
*
from
t_bd_item_info
where
isnull(charindex('
',item_name),0)
>
0 go
6、查询名称的单引号：select
*
from
t_bd_item_info
where
charindex(char(39),item_name)
>
0
go
7、查询名称的双单引号：select
*
from
t_bd_item_info
where
charindex(char(34),item_name)
>
0
go
扩展资料
1、处理名称有退格键
update
t_bd_item_info
set
item_name
=
replace(item_name,char(8),'')
where
charindex(char(9),item_name)
>
0
go
2、处理名称有制表符tab
update
t_bd_item_info
set
item_name
=
replace(item_name,char(9),'')
where
charindex(char(9),item_name)
>
0
go
3、处理名称有换行

update
t_bd_item_info
set
item_name
=
replace(item_name,char(10),'')
where
charindex(char(10),item_name)
>
0
go
4、处理名称有回车

update
t_bd_item_info
set
item_name
=
replace(item_name,char(13),'')
where
charindex(char(13),item_name)
>
0
go
5、处理名称的空格（前空格、后空格、所有空格）
update
t_bd_item_info
set
item_name
=
replace(rtrim(ltrim(item_name)),'
','')

where
isnull(charindex('
',item_name),0)
>
0 go
6、处理名称的单引号
update
t_bd_item_info
set
item_name
=
replace(item_name,char(39),'')
where
charindex(char(39),item_name)
>
0
go
7、处理名称的双单引号
update
t_bd_item_info
set
item_name
=
replace(item_name,char(34),'')
where
charindex(char(34),item_name)
>
0
go
参考资料：百度百科-结构化查询语言（SQL）

Answer 2

首先选择一张表
其次明确要查询的字段
select
字段名称
from
表名
where
字段名称
is
null