sql如何对字符和null进行连接

[zyip]

declare @a as nvarchar(50)
declare @b as nvarchar(50)
declare @c as nvarchar(50)
set @a=N'aa';
--set @b=N'';
set @c=@a + @b
select @c

[fanzhouqi]

使用 isnull（@a，''）转化一下

[jiangshun]

set @b=N'';
给个初始值，或者isnull

[guguda2008]

declare @a as nvarchar(50)
declare @b as nvarchar(50)
declare @c as nvarchar(50)
set @a=N'aa';
--set @b=N'';
set @c=ISNULL(@a,'') + ISNULL(@b,'')
select @c
--aa

[soft_wsx]

declare @a as nvarchar(50)
declare @b as nvarchar(50)
declare @c as nvarchar(50)
set @a=N'aa';
set @b=null;
set @c=ISNULL(@a,'') + ISNULL(@b,'')
select @c
--aa

加isnull处理,判断当@a或@b或NULL(不等于空值)时，赋于空值''
如果不加的话值是无法确定的！