sql:日期操作注意的,如果以字符串转日期时的函数,因为数据量大,会出问题

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---1.以日期字符操作转换日期 如果是VIP1生日不对，可以以上传的数据日期为生日 begin declare @NowBirthday datetime, @birthday  datetime,@stat datetime,@end datetime,@statbirthday datetime,@endbirthday datetime,@thirdbirthday datetime,@firthbirthday datetime, @year int,@month int , @day int,@str varchar(80),@total decimal,@vipno nvarchar(10),@now datetime   declare @smonth varchar(2),@sday varchar(2) set @vipno='174030' set @now=getdate() select @birthday=birthday from vip1 where vipno=@vipno and birthday is not null if isdate(@birthday)=0 or @birthday='1900-01-01' begin     select  @birthday=VipBirthdayDate from VipBirthdayAward where VipBirthdayNo=@vipno end set @year=Year(@now) if month(@now)=1 and month(@birthday)=12 begin    set @year=@year-1 end if month(@now)=1 and month(@birthday)=11 begin    set @year=@year-1 end if month(@now)=2 and month(@birthday)=12 begin    set @year=@year-1 end set @month=month(@birthday) set @day=day(@birthday) set @smonth=cast(@month as varchar(2)) select @smonth set @sday=cast(@day as varchar(2)) if len(@smonth)<2 begin   set @smonth='0'+@smonth   select @smonth end if len(@sday)<2 begin   set @sday='0'+@sday end set @str=cast(@year as varchar(4))+'/'+@smonth+'/'+@sday+' 00:00:00' set @NowBirthday=convert(datetime,@str) -----cast(@str as datetime) if isdate(@NowBirthday)=0 begin    select @NowBirthday='2014/01/01 00:00:00' end select @NowBirthday end GO   ---2 时间加减操作 SELECT DATEADD(yy, DATEDIFF(yy,0,getdate()), 0)     begin declare @NowBirthday datetime, @birthday  datetime,@stat datetime,@end datetime,@statbirthday datetime,@endbirthday datetime,@thirdbirthday datetime,@firthbirthday datetime, @year int,@month int , @day int,@str varchar(80),@total decimal,@vipno nvarchar(10),@now datetime,@setyear datetime   declare @smonth varchar(2),@sday varchar(2) set @vipno='174030' set @now=getdate() set @setyear=@now select @birthday=birthday from vip1 where vipno=@vipno and birthday is not null if isdate(@birthday)=0 or @birthday='1900-01-01' begin     select  @birthday=VipBirthdayDate from VipBirthdayAward where VipBirthdayNo=@vipno end set @year=Year(@now) if month(@now)=1 and month(@birthday)=12 begin    set @year=@year-1    set @setyear=DATEDIFF(year,-1,@now)    select @setyear end if month(@now)=1 and month(@birthday)=11 begin    set @year=@year-1    set @setyear=DATEDIFF(year,-1,@now)    select @setyear end if month(@now)=2 and month(@birthday)=12 begin    set @year=@year-1    set @setyear=DATEDIFF(year,-1,@now)    select @setyear end select @birthday as 'birthday' set @month=month(@birthday) select @month set @setyear=DATEADD(year, DATEDIFF(year,0,@setyear), 0) set @setyear=Dateadd(month,@month-1,@setyear) select @setyear   set @day=day(@birthday) set @setyear=Dateadd(day,@day-1,@setyear) select @NowBirthday=@setyear if isdate(@NowBirthday)=0 begin    select @NowBirthday=DATEADD(yy, DATEDIFF(yy,0,getdate()), 0) end select @NowBirthday end GO