SQL Server中的case的用法一：
Select top 100 State,JoinState, 
(
case
when State=1 and Joinstate=0 then 2
when State=1 and JoinState=1 then 1
else 0
end
) as usestate
from UserInfo
用法二：
Select Name，Age,
(
case Sex
when '男' then '先生'
when '女' then '小姐'
end
) as Sex
from User