sqlServer 求当前周的第一天和最后一天，当前月的第一天和最后一天，前三个月的第一天和今天

---当前周的第一天
select CONVERT(varchar(100),DATEADD(day,-(DATEPART(weekday,GETDATE())-1),GETDATE()) , 23)as‘周一‘,
CONVERT(varchar(100),DATEADD(day,-(DATEPART(weekday,GETDATE())-7),GETDATE()),23) as‘周日‘,
--求本月
CONVERT(varchar(100),dateadd(dd,-day(getdate())+1,getdate()),23) as‘本月第一天‘,
CONVERT(varchar(100),dateadd(ms,-3,DATEADD(mm, DATEDIFF(m,0,getdate())+1, 0)),23) as ‘本月最后一天‘ ,
CONVERT(int, CONVERT(varchar(10),DATEADD(m,-2 ,dateadd(dd,-day(getdate())+1,getdate())) ,112)) as‘前三个月‘,
--最近三个月
CONVERT(varchar(100),dateadd(ms,-3,DATEADD(mm, DATEDIFF(m,0,getdate())+1, 0)),23) as ‘本月最后一天‘