Convert row to column when data are not numbers - sql

Question

I have a Question table, which has a unknown number of questions.(first table in the figure)
I also have an AnswerSheet table, which records student's answer to question.(second table in the figure)
Create table Question
(
Id int,
Text nvarchar(50),
PRIMARY KEY (Id)
)
Create table AnswerSheet
(
StudentId int,
QuestionId int,
Answer nvarchar(50),
PRIMARY KEY (StudentId,QuestionId),
FOREIGN KEY (QuestionId) REFERENCES Question (Id)
)
insert into Question
values(1,'What''s your age'),
(2,'What''s your gender'),
(3,'When do you go home'),
....
insert into AnswerSheet
values(500,1,'20'),
(500,2,'Male'),
(500,3,'5:00pm'),
(501,1,'50'),
(502,2,'I don''t know##'),
....
How do I write a SQL to generate a table like this?
StudentId What's your age What's your gender When do you go home ...
--------- ---------------- ------------------- -------------------
500 20 Male 5:00pm ...
501 50 NULL NULL
502 NULL I don''t know## NULL ...
I feel Pivot is promising but I'm not sure how to use it especially PIVOT requires an aggreation function but my data are not numbers.

Answer 1

Assuming you wanted to go Dynamic
Example
Declare #SQL varchar(max) = Stuff((Select ',' + QuoteName(Text) From Question Order by ID For XML Path('')),1,1,'')
Select #SQL = '
Select *
From (
Select StudentID
,Col = B.Text
,Value = A.Answer
From AnswerSheet A
Join Question B on A.QuestionID=B.ID
) A
Pivot (max(Value) For [Col] in (' + #SQL + ') ) p'
Exec(#SQL);
Returns
StudentID What's your age What's your gender When do you go home
500 20 Male 5:00pm
501 50 NULL NULL
502 NULL I don't know## NULL
If it Helps, the Generated SQL Looks Like This
Select *
From (
Select StudentID
,Col = B.Text
,Value = A.Answer
From AnswerSheet A
Join Question B on A.QuestionID=B.ID
) A
Pivot (max(Value) For [Col] in ([What's your age],[What's your gender],[When do you go home]) ) p

Answer 2

I know this question is answered by accepted one, but I hope this approach helps others.
simply you can achieve your goal without using Pivot, via using Group by as next:-
Select b.StudentId,
Min(Case a.text When 'What''s your age' Then b.answer End) 'What''s your age',
Min(Case a.text When 'What''s your gender' Then b.answer End) 'What''s your gender',
Min(Case a.text When 'When do you go home' Then b.answer End) 'When do you go home'
from Question a inner join AnswerSheet b
on a.id = b.Questionid
Group By StudentId
and you mentioned unknown number of questions, so the next code for dynamic:-
DECLARE #DynamicQuestions VARCHAR(8000)
SELECT #DynamicQuestions = Stuff(
(SELECT N' Min(Case a.text When''' + replace (Text,'''','''''')
+ ''' Then b.answer End) '''
+ replace (Text,'''','''''') + ''','
FROM Question FOR XML PATH(''),TYPE)
.value('text()[1]','nvarchar(max)'),1,1,N'')
select #DynamicQuestions =
left(#DynamicQuestions,len(#DynamicQuestions)-1) -- for Removing last comma
exec ('Select b.StudentId, '+ #DynamicQuestions +
'from Question a inner join AnswerSheet b
on a.id = b.Questionid
Group By StudentId' )
Result:-
StudentId What's your age What's your gender When do you go home
500 20 Male 5:00pm
501 50 NULL NULL
502 NULL I don't know## NULL