当前时间周的起始日期（以周一为例）select DATEADD(week,DATEDIFF(week,0,getdate()),0)
上周起始：select dateadd(week,-1,DATEADD(week,DATEDIFF(week,0,getdate()),0))
上上周起始：select dateadd(week,-2,DATEADD(week,DATEDIFF(week,0,getdate()),0))
上上上周起始：select dateadd(week,-3,DATEADD(week,DATEDIFF(week,0,getdate()),0))

周七以此类推