sqlserver对字段出现NULL值的处理

-判断某些字段是否为空
--case
select case when 字段名 is null then \N else convert(varchar(20),字段名) end as NewName
select case when null is null then \N else convert(varchar(20),null) end as NewName

--SQL Server 2005：coalesce
select coalesce(字符串类型字段,\N) as NewName
select coalesce(convert(varchar(20),非字符串类型字段),\N) as NewName
select coalesce(convert(varchar(20),null),\N) as NewName

--coalesce,返回其参数中的第一个非空表达式
select Coalesce(null,null,1,2,null)union
select Coalesce(null,11,12,13,null)union
select Coalesce(111,112,113,114,null)