SQL SERVER中根据身份证号获取出生日期

create function [dbo].[f_getBirthdayByIDCard]
(@idcard varchar(18))
returns datetime
as
begin
declare @Idlen numeric(2,0),
 @birth varchar(10)
set @idlen=len(@idcard)
If @idlen=15 and SUBSTRING(@idcard,7,2)>0 and SUBSTRING(@idcard,9,2)< 13 and 
SUBSTRING(@idcard,11,2) <32
 
set @birth='19'+SUBSTRING(@idcard,7,2)+'-'+SUBSTRING(@idcard,9,2)+'-'+SUBSTRING(@idcard,11,2)

if @idlen=18 and SUBSTRING(@idcard,11,2) < 13 and SUBSTRING(@idcard,13,2)< 32
and SUBSTRING(@idcard,7,4)> 0

set @birth=SUBSTRING(@idcard,7,4)+'-'+SUBSTRING(@idcard,11,2)+'-'+SUBSTRING(@idcard,13,2)
If len(@birth) <> 10 
set @birth='1900-01-01'
return cast( convert(char(10),@birth)  as datetime)
end