Concat the table records based on the condtion - sql-server

Question

I am building a SSRS Report to show Student Class Information.
I have a table named class with information regarding classes students were attended.
My requirement is to show the days in which the classes occur. For eg: If Column Name Monday = 'Y' then I have to show the day as [Mon]. I have tried below code .
SELECT
case when Monday ='Y' then'[Mon]' else '' end +case when Monday ='Y' then ',' else '' end +
case when Tuesday ='Y' then'[Tue]' else '' end +case when Tuesday ='Y' then ','else '' end +
case when Wednesday='Y' then'[Wed]' else '' end +case when Wednesday ='Y' then ',' else '' end +
case when Thursday ='Y' then'[Thu]' else '' end +case when Thursday ='Y' then ',' else '' end +
case when Friday ='Y' then'[Fri]' else '' end +case when Friday ='Y' then ',' else '' end +
case when Saturday ='Y' then'[Sat]' else '' end +case when Saturday ='Y' then ',' else '' end +
case when Sunday ='Y' then'[Sun]' else '' end as classday
FROM vw_Class_Without_Instructor
I got the output as below.
In output there is an extra comma at the end of each line. Any way to exclude it in the select statement itself?. Is there any other way to get the output?. Use of case statements seems to be slow down the execution.

Answer 1

Please try this below query
SELECT
SUBSTRING(case when Monday ='Y' then',[Mon]' else '' end +
case when Tuesday ='Y' then',[Tue]' else '' end +
case when Wednesday='Y' then',[Wed]' else '' end +
case when Thursday ='Y' then',[Thu]' else '' end +
case when Friday ='Y' then',[Fri]' else '' end +
case when Saturday ='Y' then',[Sat]' else '' end +
case when Sunday ='Y' then',[Sun]' else '' end, 2,200) as classday
FROM vw_Class_Without_Instructor
trick: I've added commas with text so no half number of case evaluations. With ,[Mon] value I've ensured that there is always a comma in beginning which is removed using SUBSTRING.
be wise to choose a very high value in last part parameter of SUBSTRING so that it return everything starting from the charindex in second part.
See msdn reference: https://msdn.microsoft.com/en-us/library/ms187748.aspx
If the sum of start and length is greater than the number of
characters in expression, the whole value expression beginning at
start is returned.

Answer 2

You can try this;
select
CASE WHEN LEN(classday_with_comma) > 0 THEN LEFT(classday_with_comma,LEN(classday_with_comma) - 1) ELSE '' END as classday
From (
SELECT
case when Monday = 'Y' then '[Mon],' else '' end +
case when Tuesday = 'Y' then '[Tue],' else '' end +
case when Wednesday = 'Y' then '[Wed],' else '' end +
case when Thursday = 'Y' then '[Thu],' else '' end +
case when Friday = 'Y' then '[Fri],' else '' end +
case when Saturday = 'Y' then '[Sat],' else '' end +
case when Sunday = 'Y' then '[Sun],' else '' end as classday_with_comma
FROM vw_Class_Without_Instructor
) as x
Two case statement can be truncated to one from
case when Monday ='Y' then'[Mon]' else '' end +
case when Monday ='Y' then ',' else '' end +
To
case when Monday = 'Y' then '[Mon],' else '' end +
And
LEFT(classday_with_comma, LEN(classday_with_comma) - 1)
will remove the last ,