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

---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