-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)