请教个 sql 问题，通过这个 sql 怎么写个函数

select distinct case ISNULL(p.iscomment,0) when 0 then '未评价' else '已评价' end zhuangtai from piproject p
left join PiEntpriseContacts s on p.entpriseid=s.entpriseid and s.enableflag=1
where 1=1 and p.enableflag=1 and (p.estate = 13 or p.PassNodeId=11313)
and p.CreateOn > dateadd(month,-3,GETDATE()) and (p.Mobile = '{0}' or s.mobile='{0}') and p.iscomment is null


{0}为变量