TSQL - char changing to INT - sql

Question

I need the variable #end_period be character e.g. 01 and not 1
What is wrong with the following code?
DECLARE #start_year AS CHAR(4)
DECLARE #end_year AS CHAR(4)
DECLARE #start_period AS CHAR(2)
DECLARE #end_period AS CHAR(2)
DECLARE #start_date as datetime
DECLARE #end_date as datetime
SET #start_year = '2014'
SET #end_year = '2014'
SET #start_period = '07'
SET #end_period = '08'
SET #end_year = CASE WHEN #end_period ='12' THEN #end_year + 1 ELSE #end_year END
SET #end_period = CASE WHEN #end_period ='12' THEN '01' ELSE #end_period + 1 END
select #end_year
select #end_period

Answer 1

There's something weird about using CHAR. I don't know why but when I do this, I get your desired results:
DECLARE #start_year AS CHAR(4)
DECLARE #end_year AS CHAR(4)
DECLARE #start_period AS CHAR(2)
DECLARE #end_period AS CHAR(2)
DECLARE #start_date as datetime
DECLARE #end_date as datetime
SET #start_year = '2014'
SET #end_year = '2014'
SET #start_period = '07'
SET #end_period = '08'
SET #end_year = CASE WHEN #end_period ='12' THEN #end_year + 1 ELSE #end_year END
SET #end_period = CASE WHEN #end_period ='12' THEN '01' ELSE RIGHT('0'+CAST((#end_period + 1) AS varchar(2)) ,2) END
select #end_year
select #end_period
However when I change this: CAST((#end_period + 1) AS varchar(2))
To this: CAST((#end_period + 1) AS char(2))
I just get a '9' instead of '09'. Weird. I don't know why.
EDIT: MYSTERY SOLVED.
I don't know why I didn't think of this right away. Actually, I do. It's only 9 am.
The '9' that you are seeing as a result is actually '9 ' (9 with a blank space after it) because char(2) has to have 2 characters in it. So doing RIGHT('0'+'9 ') is of course going to return '9 '. You could use RTRIM() or REPLACE() to get rid of the space while preceding it with a zero if you want, or you can just use the varchar cast I illustrated above.

Answer 2

When you do :
#end_period + 1
Example :
'08'+1
The string '08' is converted to the integer 8, one is added, result => 9.
An implicit conversion is then made back to char(2), which is '9'.
The full matrix of possible conversions (implicit or explicit) can be found on MSDN.
To solve your problem, you can then add leading zeroes this way :
SET #end_period = CASE WHEN #end_period ='12' THEN '01' ELSE RIGHT('00' + CAST((#end_period + 1) as VARCHAR(2)), 2) END

Answer 3

Try
SET #end_period = CASE WHEN #end_period = '12' THEN '01'
ELSE CASE WHEN #end_period > 8 THEN CONVERT(VARCHAR,#end_period + 1)
ELSE '0' + CONVERT(VARCHAR,#end_period + 1)
END
END