SQL SERVER 取本月上月日期

1. select   dateadd(dd,-day(dateadd(month,-1,getdate()))+1,dateadd(month,-1,getdate()))     /*上个月一号*/  
2. select   dateadd(dd,-day(getdate()),getdate())                                                                      /* 上月月底 */  
3. select   dateadd(dd,-day(getdate())+1,getdate())                                                                  /* 本月一号 */  
4. select   dateadd(dd,-day(dateadd(month,1,getdate())),dateadd(month,1,getdate()))            /* 本月底 */  
5. select   dateadd(dd,-day(dateadd(month,1,getdate()))+1,dateadd(month,1,getdate()))        /* 下月一号 */  
6. select   dateadd(dd,-day(dateadd(month,2,getdate())),dateadd(month,2,getdate()))            /* 下月月底 */