-判斷某些字段是否為空
--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('字符串類型字段','/N') as 'NewName'
select coalesce(convert(varchar(20),'非字符串類型字段'),'/N') as 'NewName'
select coalesce(convert(varchar(20),null),'/N') as 'NewName'

--coalesce,返回其參數(shù)中的第一個(gè)非空表達(dá)式
select Coalesce(null,null,1,2,null)union
select Coalesce(null,11,12,13,null)union
select Coalesce(111,112,113,114,null)