TSQL - converting date string to datetime - sql

Question

I have a table that has the following column (with some sample entries provided):
COLUMN NAME: pt_age_old
20 Years 8 Months 3 Weeks
1 Year 3 Months 2 Weeks
58 Years 7 Months
1 Year
7 Years 11 Months 2 Weeks
26 Years 6 Months
56 Years 6 Months
48 Years 6 Months 4 Weeks
29 Years 11 Months
4 Years 3 Months
61 Years 8 Months 4 Weeks
I have tried to cast it to datetime, of course this did not work. Same with convert.
Keep getting the following message:
Msg 241, Level 16, State 1, Line 2
Conversion failed when converting date and/or time from character string.
Main 2 questions are:
Is this type of conversion even possible with this existing string format?
If so, can you steer me in the right direction so I can make this happen?
Thanks!

Answer 1

This could be done using custom code such as below - I've assumed the values you're using are people's ages, and you're trying to work out their date of birth given their age today.
You can see the below code in action here: http://sqlfiddle.com/#!3/c757c/2
create function dbo.AgeToDOB(#age nvarchar(32))
returns datetime
as
begin
declare #pointer int = 0
, #pointerPrev int = 1
, #y nvarchar(6)
, #m nvarchar(6)
, #w nvarchar(6)
, #d nvarchar(6)
, #result datetime = getutcdate() --set this to the date we're working to/from
--convert various ways of expressing units to a standard
set #age = REPLACE(#age,'Years','Y')
set #age = REPLACE(#age,'Year','Y')
set #age = REPLACE(#age,'Months','M')
set #age = REPLACE(#age,'Month','M')
set #age = REPLACE(#age,'Weeks','W')
set #age = REPLACE(#age,'Week','W')
set #age = REPLACE(#age,'Days','D')
set #age = REPLACE(#age,'Day','D')
set #pointer = isnull(nullif(CHARINDEX('Y',#age),0),#pointer)
set #y = case when #pointer > #pointerprev then SUBSTRING(#age,#pointerprev,#pointer - #pointerprev) else null end
set #pointerPrev = #pointer + 1
set #pointer = isnull(nullif(CHARINDEX('M',#age),0),#pointer)
set #m = case when #pointer > #pointerprev then SUBSTRING(#age,#pointerprev,#pointer - #pointerprev) else null end
set #pointerPrev = #pointer + 1
set #pointer = isnull(nullif(CHARINDEX('W',#age),0),#pointer)
set #w = case when #pointer > #pointerprev then SUBSTRING(#age,#pointerprev,#pointer - #pointerprev) else null end
set #pointerPrev = #pointer + 1
set #pointer = isnull(nullif(CHARINDEX('D',#age),0),#pointer)
set #d = case when #pointer > #pointerprev then SUBSTRING(#age,#pointerprev,#pointer - #pointerprev) else null end
set #result = dateadd(YEAR, 0 - isnull(cast(#y as int),0), #result)
set #result = dateadd(MONTH, 0 - isnull(cast(#m as int),0), #result)
set #result = dateadd(Week, 0 - isnull(cast(#w as int),0), #result)
set #result = dateadd(Day, 0 - isnull(cast(#d as int),0), #result)
return #result
end
go
select dbo.AgeToDOB( '20 Years 8 Months 3 Weeks')
NB: there's a lot of scope for optimisation here; I've left it simple above to help keep it clear what's going on.

Answer 2

Technically it is possible to convert the relative time label into a datetime, but you will need a reference date though (20 Years 8 Months 3 Weeks as of '2013-10-16'). The reference date is most likely today (using GETDATE() or CURRENT_TIMESTAMP), but there is a chance it is a different date. You will have to parse the label, convert it to a duration, and then apply the duration to the reference time. This will be inherently slow.
There are at least two possible ways of doing this, write a FUNCTION to parse and convert the relative time label or use a .NET extended function to do the conversion. You would need to identify all of the possible labels otherwise the conversion will fail. Keep in mind that the reference date is important since 2 months is not a constant number of days (Jan-Feb = either 58 or 59 days).
Here is a sample of what the function might look like:
-- Test data
DECLARE #test varchar(50)
, #ref_date datetime
SET #test = '20 Years 8 Months 3 Weeks'
SET #ref_date = '2013-10-16' -- or use GETDATE() / CURRENT_TIMESTAMP
-- Logic in function
DECLARE #pos int
, #ii int
, #val int
, #label varchar(50)
, #result datetime
SET #pos = 0
SET #result = #ref_date
WHILE (#pos <= LEN(#test))
BEGIN
-- Parse the value first
SET #ii = NULLIF(CHARINDEX(' ', #test, #pos), 0)
SET #label = RTRIM(LTRIM(SUBSTRING(#test, #pos, #ii - #pos)))
SET #val = CAST(#label AS int)
SET #pos = #ii + 1
-- Parse the label next
SET #ii = NULLIF(CHARINDEX(' ', #test, #pos), 0)
IF (#ii IS NULL) SET #ii = LEN(#test) + 1
SET #label = RTRIM(LTRIM(SUBSTRING(#test, #pos, #ii - #pos)))
SET #pos = #ii + 1
-- Apply the value and offset
IF (#label = 'Days') OR (#label = 'Day')
SET #result = DATEADD(dd, -#val, #result)
ELSE IF (#label = 'Weeks') OR (#label = 'Week')
SET #result = DATEADD(ww, -#val, #result)
ELSE IF (#label = 'Months') OR (#label = 'Month')
SET #result = DATEADD(mm, -#val, #result)
ELSE IF (#label = 'Years') OR (#label = 'Year')
SET #result = DATEADD(yy, -#val, #result)
END
SELECT #result
-- So if this works correctly,
-- 20 Years 8 Months 3 Weeks from 2013-10-16 == 1993-01-26

Answer 3

Make a function to split it up:
create function f_tst
(
#t varchar(200)
) returns date
begin
declare #a date = current_timestamp
;with split1 as
(
select 1 start, charindex(' ', #t + ' ', 4)+1 stop
where #t like '% %'
union all
select stop, charindex(' ', #t + ' ', stop + 4)+1
from split1
where charindex(' ', #t, stop) > 0
), split2 as
(
select cast(left(x.sub, charindex(' ', x.sub)) as int) number,
substring(x.sub, charindex(' ', x.sub) + 1, 1) unit
from split1
cross apply (select substring(#t, start, stop - start) sub) x
)
select #a = case unit when 'W' then dateadd(ww, -number, #a)
when 'Y' then dateadd(yy, -number, #a)
when 'M' then dateadd(mm, -number, #a)
end
from split2
return #a
end
Test function:
select dbo.f_tst(age)
from (values('20 Years 8 Months 3 Weeks'),('1 Month') ) x(age)
Result:
1993-01-27
2013-09-17

Answer 4

No, date time type presents actual date, like YYYY-MM-DD HH:MM, your strings are not DATE fields, they are age, to have date time you need date of birth and them somehow add this age to it