SQL Server function with count doesn't work as intended - sql

Question

I am working on a project for class & course management. I want to create a function that automatically creates a course code based on the course name and then adds a number based on whether there already exist a course name with the same first 4 characters.
Here is what my function looks like:
CREATE FUNCTION [dbo].[fxGenerateCourseCode]
(#course_name VARCHAR(50))
RETURNS VARCHAR(8)
AS
BEGIN
DECLARE #course_code VARCHAR(8), #count_course INT
SET #count_course = (SELECT COUNT(1) FROM dbo.COURSE_TB
WHERE SUBSTRING(course_name, 1, 4) = SUBSTRING(#course_name, 1, 4)) + 1
SELECT #course_code = UPPER(SUBSTRING(#course_name, 1, 4)) + ' - ' + '00' + CAST(#count_course AS VARCHAR)
RETURN #course_code
END
The problem is, whenever I execute this function, it is not returning the right count values and it doesn't include the 00 either.
For example, executing this:
SELECT dbo.fxGenerateCourseCode('french')
returns FREN-0 rather than FREN-001 (which is what I expect).
However, when I execute the code manually, it gives me the result that I expect:
DECLARE #course_code VARCHAR(8), #count_course INT, #course_name VARCHAR(50)
SET #course_name = 'french'
SET #count_course = (SELECT COUNT(1) + 1 FROM dbo.PARAMETRES_COURS
WHERE SUBSTRING(nom_cours, 1, 4) = SUBSTRING(#course_name, 1, 4))
SELECT course_code = UPPER(SUBSTRING(#course_name, 1, 4)) + ' - ' + '00' + CAST(#count_course AS VARCHAR)
Result: FREN-001.
I have tried changing the way I write the function with not much result. Can someone help me know where the problem here is coming from? Am I doing something wrong in the function?
Thank you

Answer 1

I suspect that you are putting the value into a column with a length of 6. That said, the problem would appear to be the spaces around the hyphen. Also, always include a length for varchar, because the defaut length varies by context and it might not do what you want:
You can simplify your code and make it more accurate:
declare #course_code varchar(8), #count_course int;
select #count_course = count(1) + 1
from dbo.COURSE_TB
where left(course_name, 4) = left(#course_name, 4);
select #course_code = concat(left(upper(#course_name, 4)), '-', '00', #count_course);
Note that this still doesn't do what you want, which is padding the number. This version only works for 9 courses. You seem to want:
select #course_code = concat(left(upper(#course_name, 4)), '-',
right(concat('00', #count_course), 3)
);
Note the use of the concat() function, so you don't have to worry about lengths of strings when doing a conversion.