Can I use a WHILE loop inside a SQL SELECT Query - sql

Question

I need to create a formatted text (CSV) output with an even number of columns from a SQL query of two tables that do not have the same number of elements. I can't seem to pad the data to the required number of columns.
Sample Data
table Students(id, name)
values
(1, Alex),
(2, Bob),
(3, Charlie),
(4, David)
table Hobbies (studentId, hobby)
values
(2,'skating')
(2,'sailing')
(3,'reading')
(4,'video games')
(4,'paintball')
(4,'nascar')
(4,'baseball')
Desired Output
[ID][OutputString]
[0][Student,Hobby1,Hobby2,Hobby3,Hobby4]
[1][Alex,,,,]
[2][Bob,skating,sailing,]
[3][Charlie,reading,,,]
[4][David,video games,paintball,nascar,baseball]
Broken PseudoCode
DECLARE #maxHobbies INT = 4;
DECLARE #hobbyCount INT = 1;
DECLARE headerString varchar(max) = 'Student';
WHILE #hobbyCount <= #maxHobbies
BEGIN
set #headerString = #headerString + ',Hobby' + #hobbyCount
#hobbyCount = #hobbyCount + 1
END
DECLARE #outputString varchar(max)
SET #outputString = concat(#headerSting, char(13)) +
SELECT 0 AS ID, #headerString AS OutputString
UNION
SELECT
id,
name + (WHILE #hobbyCount <= #maxHobbies BEGIN
(CASE
WHEN EXISTS SELECT hobby FROM Hobbies where studentId = Students.id
THEN ',' + SELECT hobby FROM Hobbies where studentId = Students.id
ELSE ','
END)
END)
FROM Students

Answer 1

You want up to 4 hobbies. You can do this with conditional aggregation:
select s.id,
(s.name + ',' +
max(case when seqnum = 1 then h.hobby else '' end) + ',' +
max(case when seqnum = 2 then h.hobby else '' end) + ',' +
max(case when seqnum = 3 then h.hobby else '' end) + ',' +
max(case when seqnum = 4 then h.hobby else '' end)
) as outputstring
from students s left join
(select h.*,
row_number() over (partition by h.studentid order by (select null)) as seqnum
from hobbies h
) h
on h.studentid = s.id
group by s.id, s.name;