date problem

I am trying to subtract a month from a YearMonth format. YYYYMM YearMonth is is varchar format.

So I do :

select yearmonth - 1 from tableA

The problem is when get to 200601 it returns 200600 instead of 200512

Any suggestion how to fix this?
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asked Oct 25, 2011 at 07:30 AM in Default

sqlnewb gravatar image

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1 answer: sort voted first

To do date arithmetic on the field, you need to turn it into a date

Follow this code

declare @YYYYMM varchar(6)
set @YYYYMM = '200601'

 convert(datetime, @YYYYMM+'01', 112),
 dateadd(mm, -1, convert(datetime, @YYYYMM+'01', 112)),
 convert(varchar, dateadd(mm, -1, convert(datetime, @YYYYMM+'01', 112)),112),
 left(convert(varchar, dateadd(mm, -1, convert(datetime, @YYYYMM+'01', 112)),112),6)

I first string concatenate a '01' to make a string that matches the date format of 112 (ISO standard). Then I can convert that to an actual date, then subtract one month using DATEADD, convert it back to a string from the 112 style date, and finally remove the last 2 characters to get your YYYYMM format back again.

The last one is the one you need, but I've shown the intermediary steps to help you understand the path....
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answered Oct 25, 2011 at 07:40 AM

Kev Riley gravatar image

Kev Riley ♦♦
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Thanks that makes sense. Thank for the explanation as well
Oct 25, 2011 at 07:48 AM sqlnewb
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asked: Oct 25, 2011 at 07:30 AM

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Last Updated: Oct 25, 2011 at 07:30 AM