怎么检索为空的数据(text类型)

[newslxw]

我想将a表中的字段content为null的全部检索出来
我试了一下用select * from a where isnull(content)和select * from a where isempty(content)但发现都不行
content为text类型

[zjcxc]

select * from a where content is null

[zjcxc]

--如果要把0长度的也检索出来,就用:
select * from a where datalength(content)=0

[zjcxc]

--上面的要改一下,如果要把0长度的也检索出来,就用:

select * from a where content is null or datalength(content)=0

[yjbnew]

select * from a where content is null or content=''

[yjbnew]

select * from a where content is null or trim(content)=''