Calculating age from SSN - sql-server

Question

I'm working with a project in SSRS
In Database i have a column called X and in this column , i have Social Security Numbers for all employees and all numbers look like this with out any ( - or /) example 1111111111 (DDMMYYXXXX).
My question is ,how can i write a sql to just select 6 first number and then minus current time and in end give me age of employees. Can someone please point me in the right direction.
Thanks.
So far the sql i wrote look like this:
create function dbo.birthdate_from_cpr(#cpr varchar(10))
returns date
as
begin
declare #year char(2) = substring(#cpr, 5, 2),
#month char(2) = substring(#cpr, 3, 2),
#day char(2) = substring(#cpr, 1, 2),
#century char(2)
if right(datepart(yy, getdate()), 2) < #year
set #century = left(datepart(yy, getdate()) - 100, 2)
else
set #century = left(datepart(yy, getdate()), 2)
return convert(date, #century + #year + #month + #day, 120)
end
go
select dbo.birthdate_from_cpr('1312761234'),
dbo.birthdate_from_cpr('0101041234'),
age = datediff(yy, dbo.birthdate_from_cpr('1312761234'), getdate())

Answer 1

One way is to use left and stuff to create a well-formatted string, and convert to change it to a date value, and then it's just datediff.
Don't be alarmed by the length of the query, It's only the last column you need. I've chosen to show every step in a different column.
DECLARE #SSN char(10) = '1309761234'
SELECT #SSN as OriginalString,
STUFF(
STUFF(LEFT(#SSN, 6), 3, 0, '.')
, 6, 0, '.') As DateString,
CONVERT(date,
STUFF(
STUFF(LEFT(#SSN, 6), 3, 0, '.')
, 6, 0, '.')
, 4) As Date, -- German, no century - dd.mm.yy
DATEDIFF(YEAR,
CONVERT(date,
STUFF(LEFT(#SSN, 4), 3, 0, '.') +'.'+
CAST(DATEPART(YEAR, GETDATE()) / 100 - 1 as char(2)) +
SUBSTRING(#SSN, 5, 2)
, 104)
, GETDATE()) As Age
Result:
OriginalString DateString Date Age
1309761234 13.09.76 13.09.1976 00:00:00 41
And with your query:
SELECT Users.Id, Users.FirstName + ' ' + Users.LastName AS Medarbajder,
Users.SSN AS CPRNR,
CASE WHEN Users.SSN IS NOT NULL THEN
DATEDIFF(YEAR,
CONVERT(date,
STUFF(LEFT(Users.SSN, 4), 3, 0, '.') +'.'+
CAST(DATEPART(YEAR, GETDATE()) / 100 - 1 as char(2)) +
SUBSTRING(Users.SSN, 5, 2)
, 104)
, GETDATE())
ELSE
NULL
END As Age,
convert(varchar(10), Paychecks.WorkStartDate, 105) AS StartDato ,
Paychecks.DepartmentName AS Afdelinger
FROM dbo.Paychecks, dbo.Users
WHERE Users.CustomerId=214 AND Users.Id=Paychecks.UserId order by Users.FirstName;

Answer 2

You need to extract the date from the ssn column to calculate the age, assuming your described format "1111111111 (DDMMYYXXXX)". However the format string DDMMYY won't easily convert by itself so we need to flip it around into a format the CONVERT function will recognise
Something like this:
convert(date, substring(Users.SSN , 17, 2) + substring(Users.SSN , 15, 2) + substring(Users.SSN , 13, 2), 12)
From there its a simple matter to DATEDIFF the age.
Be aware that SQL Server will treat the years 00 to 49 as this century. Which might be an issue for older folk...

Answer 3

I'd recommend creating a UDF for converting the CPR to a date which will make your life easier with doing analysis in the future and you test it more easily. This version addresses the century issue that #paul-bambury mentioned by assuming nobody is more than 100 years old.
create function dbo.birthdate_from_cpr(#cpr varchar(10))
returns date
as
begin
declare #year char(2) = substring(#cpr, 5, 2),
#month char(2) = substring(#cpr, 3, 2),
#day char(2) = substring(#cpr, 1, 2),
#century char(2)
-- if the current 2 digit year is less than the birthday year, assume it was last century
-- e.g. 76 should be 1976 but 02 should be 2002
if right(datepart(yy, getdate()), 2) < #year
set #century = left(datepart(yy, getdate()) - 100, 2)
else
set #century = left(datepart(yy, getdate()), 2)
return convert(date, #century + #year + #month + #day, 120)
end
go
select dbo.birthdate_from_cpr('1312761234'),
dbo.birthdate_from_cpr('0101041234'),
age = datediff(yy, dbo.birthdate_from_cpr('1312761234'), getdate())