Inserting four columns into one - sql

Question

Good morning,
I have a table TestSeed that stores a multiple choices test with the following structure:
QNo QText QA1 QA2 QA3 QA4
It already contains data.
I would like to move some of the columns to a temp table with the following structure:
QNo QA
Where QNo will store the question number from the first table and QA will store QA1, QA2, QA3 and QA4 over four rows of data.
I am trying to do it in a SQL stored procedure. And it got down to the following situation:
I want to create a nested loop where I can go through the TestSeed table rows in the outer loop and then go through the four QA fields and insert them in the inner loop.
So my code will look something like this:
Declare #TempAnswers as table
(
[QNo] int,
[QAnswer] [nvarchar](50) NULL,
)
DECLARE #QNO int
DECLARE QROW CURSOR LOCAL FOR select QNo from #TempSeed
OPEN QROW
FETCH NEXT FROM QROW into #QNO
WHILE ##FETCH_STATUS = 0
BEGIN
DECLARE #i INT
SET #i = 1
WHILE (#i <=4)
Begin
insert into #TempAnswers
(
[QNo],
[QAnswer]
)
select QNo, 'QA'+#i --This is the part I need
from #TempSeed
SET #i = #i +1
END
FETCH NEXT FROM QROW into #QNO
END
CLOSE IDs
DEALLOCATE IDs
So I guess my question is: can I use a concatenated string to refer to a column name in SQL? and if so how?
I am sort of a beginner. I would appreciate any help I can.

Answer 1

No need for loop, you can simply use the UNPIVOT table operator to do this:
INSERT INTO temp
SELECT
QNO,
val
FROM Testseed AS t
UNPIVOT
(
val
FOR col IN([QA1], [QA2], [QA3], [QA4])
) AS u;
For example, if you have the following sample data:
| QNO | QTEXT | QA1 | QA2 | QA3 | QA4 |
|-----|-------|-----|-----|-----|-----|
| 1 | q1 | a | b | c | d |
| 2 | q2 | b | c | d | e |
| 3 | q3 | e | a | b | c |
| 4 | q4 | a | c | d | e |
| 5 | q5 | c | d | e | a |
The previous query will fill the temp table with:
| QNO | QA |
|-----|----|
| 1 | a |
| 1 | b |
| 1 | c |
| 1 | d |
| 2 | b |
| 2 | c |
| 2 | d |
| 2 | e |
| 3 | e |
| 3 | a |
| 3 | b |
| 3 | c |
| 4 | a |
| 4 | c |
| 4 | d |
| 4 | e |
| 5 | c |
| 5 | d |
| 5 | e |
| 5 | a |
SQL Fiddle Demo
The UNPIVOT table operator, will convert the values of the four columns [QA1], [QA2], [QA3], [QA4] into rows, only one row.
Then you can put that query inside a stored procedure.

Answer 2

So, to answer your last question, you can use Dynamic SQL which involves creating your query as a STRING and then executing it, in case you really want to stick to the method you already started.
You will have to declare a variable to store the text of your query:
DECLARE #query NVARCHAR(MAX)
SET #query = 'SELECT QNo, QA' + #i + ' FROM #TempSeed'
EXEC sp_executesql #query
This will have to be done everytime you build your query which is to be executed (declaration, seting the text of the query and executing it).
If you want something simpler, there are other answers here which will work.

Answer 3

Try this:
Declare #TempAnswers as table
(
[QNo] int,
[QAnswer] [nvarchar](50) NULL,
);
INSERT INTO #TempAnswers(QNo, QAnswer)
SELECT QNo, QA
FROM (SELECT QNo, QA1 AS QA FROM TestSeed
UNION
SELECT QNo, QA2 AS QA FROM TestSeed
UNION
SELECT QNo, QA3 AS QA FROM TestSeed
UNION
SELECT QNo, QA4 AS QA FROM TestSeed
) AS A
ORDER BY QNo;