Question

I think it would be quickest to show by example, so here goes a simplified version of my problem. I am using SQL Server.

This is the data model

SURVEY       QUESTION        ANSWER
------       --------        -------
surveyId     questionId      answerId
             questionText    surveyId
                             questionId
                             answerText

Here’s some sample data

SURVEY          QUESTION
 ----------      ------------ --------------
| surveyId |    | questionId | questionText |
 ----------      ------------ --------------
| 1        |    | 1          | Name         |
| 2        |    | 2          | E-Mail       |
 ----------     | 3          | Address      |
                | 4          | Phone        |
                 ------------ --------------
ANSWER
 -----------------------------------------------
| answerId | surveyId | questionId | answerText |
 -----------------------------------------------
| 1        | 1        | 1          | John       |
| 2        | 1        | 2          | [e-mail] |
| 3        | 1        | 3          | New York   |
| 4        | 1        | 4          | 1112223344 |
| 5        | 2        | 1          | Pete       |
| 6        | 2        | 2          | [e-mail] |
| 7        | 2        | 3          | Boston     |
| 8        | 2        | 4          | 5556667788 |
 -----------------------------------------------

Finally, here’s what I’d like to select

RESULT
 ------------------------------
| surveyId | name | email      |
 ------------------------------
| 1        | John | [e-mail] |
| 2        | Pete | [e-mail] |
 ------------------------------

I’d like to be able to specify at run time which columns I need in my final table. Right now I can get this result by doing the following

SELECT rName.surveyId, rName.requestor, rEmail.email 
FROM (SELECT a.answerText AS name, a.surveyId
      FROM answer a INNER JOIN question q ON a.questionId = q.questionId 
      WHERE a.surveyId = @surveyId AND q.questionText = 'Name') AS rName
INNER JOIN 
     (SELECT a.answerText AS name, a.surveyId
      FROM answer a INNER JOIN question q ON a.questionId = q.questionId 
      WHERE a.surveyId = @surveyId AND q.questionText = 'E-Mail') AS rEmail
ON rName.questionnaireId = rEmail.questionnaireId

As you can see, it’s ugly, and contains duplicate code. Is there a way to do this cleaner?

Answer 1

SELECT  a.surveyID,
        MAX(CASE WHEN c.questionText = 'Name' THEN b.answerText ELSE NULL END) name,
        MAX(CASE WHEN c.questionText = 'E-Mail' THEN b.answerText ELSE NULL END) email
FROM    Survey a
        INNER JOIN Answer b
            ON a.surveyID = b.surveyID
        INNER JOIN Question c
            ON b.questionID = c.questionID
GROUP BY a.surveyID

• See SQLFiddle Demo