Format Jagged data gained from dynamic pivot - sql

Question

I need to format and extract some data from a database. While I can extract the data successfully I am struggling with the jagged nature of it.
What I have is the following:
create table temp
(
QuestionID INT,
AnswerID INT,
AnswerValue NVARCHAR(50)
)
insert into temp values (1, 1, 'Ans C')
insert into temp values (1, 2, 'Ans B')
insert into temp values (1, 3, 'Ans A')
insert into temp values (2, 4, 'Ans D')
insert into temp values (2, 5, 'Ans E')
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX);
SET #cols = STUFF((SELECT distinct ',' + QUOTENAME(c.AnswerID)
FROM temp c
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT QuestionID, ' + #cols + ' from
(
select QuestionID
, AnswerValue
, AnswerID
from temp
) x
pivot
(
max(AnswerValue)
for AnswerID in (' + #cols + ')
) p '
execute(#query)
drop table temp
Executed this produces
+------------+-------+-------+-------+-------+-------+
| QuestionID | 1 | 2 | 3 | 4 | 5 |
+------------+-------+-------+-------+-------+-------+
| 1 | Ans C | Ans B | Ans A | NULL | NULL |
| 2 | NULL | NULL | NULL | Ans D | Ans E |
+------------+-------+-------+-------+-------+-------+
I just need to format it like this
+------------+-------+-------+-------+
| QuestionID | Q1 | Q2 | Q3 |
+------------+-------+-------+-------+
| 1 | Ans C | Ans B | Ans A |
| 2 | NULL | Ans D | Ans E |
+------------+-------+-------+-------+
Note due to restrictions this needs to be done in SQL rather than an advanced language such as c#.

Answer 1

A few things are wrong with the code. First, you are creating your column list using the AnswerID so the data is being split across multiple columns instead of the Answer for each question.
In order to fix this, you'll want to use a windowing function like row_number() to create a sequence for each question/answer combination.
When creating your dynamic columns change the code to be:
SET #cols = STUFF((SELECT ',' + QUOTENAME('Q'+cast(rn as varchar(10)))
FROM
(
SELECT rn = row_number() over(partition by QuestionID
order by AnswerID)
FROM temp
) c
group by rn
order by rn
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
This will use row_number() and will create the column names based on the QuestionID. Then you'll include the row_number() in your subquery making your code:
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
SET #cols = STUFF((SELECT ',' + QUOTENAME('Q'+cast(rn as varchar(10)))
FROM
(
SELECT rn = row_number() over(partition by QuestionID
order by AnswerID)
FROM temp
) c
group by rn
order by rn
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT QuestionID, ' + #cols + '
from
(
select QuestionID
, AnswerValue
, col = ''Q''+ cast(row_number() over(partition by QuestionID
order by AnswerID) as varchar(10))
from temp
) x
pivot
(
max(AnswerValue)
for col in (' + #cols + ')
) p '
exec sp_executesql #query;
See SQL Fiddle with Demo. This gives a result:
| QUESTIONID | Q1 | Q2 | Q3 |
|------------|-------|-------|--------|
| 1 | Ans C | Ans B | Ans A |
| 2 | Ans D | Ans E | (null) |

Answer 2

You can use this part of code:
SELECT 'A' + CAST(ROW_NUMBER() OVER(PARTITION BY QuestionID ORDER BY Answer) AS VARCHAR(10)) AS cName
FROM tblAnswers
in order to generate the column names required. The above gives you sth like:
cName
-----
A1
A2
A3
A1
A2
You can subsequently use the above in your dynamic pivot to obtain the desired result:
DECLARE #cols AS NVARCHAR(MAX), #query AS NVARCHAR(MAX);
SET #cols = STUFF((SELECT distinct ',' + QUOTENAME(a.cName)
FROM (
SELECT 'A' + CAST(ROW_NUMBER() OVER(PARTITION BY QuestionID ORDER BY Answer) AS VARCHAR(10)) AS cName
FROM tblAnswers
) a
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)'),1,1,'')
set #query = 'SELECT Question, ' + #cols + ' ' +
'FROM (
SELECT q.Question, a.Answer,
''A'' + CAST(ROW_NUMBER() OVER(PARTITION BY a.QuestionID ORDER BY Answer) AS VARCHAR(10)) AS cName
FROM tblAnswers AS a
INNER JOIN tblQuestions AS q ON a.QuestionID = q.QuestionID
) t
PIVOT
(
MAX(t.Answer)
FOR cName in (' + #cols + ')
) Pvt '
execute(#query)
Output from above looks like:
Question A1 A2 A3
-----------------------------------
Q1 Answer1 Answer2 Answer3
Q2 Answer4 Answer5 NULL
SQL Fiddle demo here