Question

I have one table that looks like this called survey_1:

================================================
|id  | token  |     1X2X1     |    1X2X2       |
=====+========+===============+================|
| 1  |   1    |    YES        | Justin Beiber  |
|----+--------+---------------+----------------|
| 2  |   1    |    YES        | Britney Spears |
|----+--------+---------------+----------------|

note: 1X2X1 represents- survey-id X group-id X question-id

I have another table called survey_questions:

===============================================================
|sid |   gid  |   qid  |             question                 |
=====+========+===============+===============================|
| 1  |  2     |    1   |  Do you listen to music?             |
|----+--------+-----------------------------------------------|
| 1  |  2     |    2   |  Who is your favorite music artists? |
|----+--------+-----------------------------------------------|

The sid (survey-id), gid (group-id) and qid(question-id) define that specific question in this table

I need a query that will give me a result like this:

======================================================
|           Question                  |   Answer     |
=========+===========+===============================|
| Do you listen to music?             |    YES       |            
|----------------------------------------------------|
| Who is your favorite music artists? | Justin Beiber| 
|----------------------------------------------------|

NOTE: My database contains thousands of these columns, so it would be very time consuming to edit every survey to match up perfectly in this format.

Can anyone help out with this? Thank you

Answer 1

You need to use ‘UNPIVOT’, which MySQL unfortunately does not support. You can do a similar thing by hardcoding the column names (but you need to know all the columns in advance) like this:

SELECT survey_questions.Question,
       CASE survey_questions.qid 
         WHEN 1 THEN survey_1.`1X2X1`
         WHEN 2 THEN survey_1.`1X2X2`
         WHEN 3 THEN survey_1.`1X2X3`
         WHEN 4 THEN survey_1.`1X2X4`
       // ...
       END as Answer
FROM survey_questions
JOIN survey_1 
  ON survey_questions.qid = survey_1.id
  AND survey_questions.gid = survey_1.token_id
WHERE survey_questions.sid = 1

Of course, you can always use some scripting language to generate the column names for you… For example, here is a stored procedure you can make:

CREATE PROCEDURE 'get_qa_for_survey'
(
  IN surveyId INT
)
BEGIN
  DECLARE query1 TEXT; 
  SET @tableName = 'survey_' + surveyId;
  SET query1 = 'SELECT survey_questions.Question,
       CASE survey_questions.qid ';

  DECLARE col_names CURSOR FOR
    SELECT column_name
    FROM INFORMATION_SCHEMA.COLUMNS
    WHERE table_name = @tableName
    AND (column_name LIKE surveyId +'X%');
    ORDER BY ordinal_position;

  select FOUND_ROWS() into num_rows;

  SET i = 1;
  the_loop: LOOP    
     IF i > num_rows THEN
        CLOSE col_names;
        LEAVE the_loop;
     END IF;

     FETCH col_names 
     INTO col_name;     
     SET query1 = query1 + ' WHEN ' + i + ' THEN ' + @tableName + '.' + col_name
     SET i = i + 1;  
  END LOOP the_loop;

  SET query1 = query1 + ' END as Answer
    FROM survey_questions
    JOIN ' + @tableName + '
      ON survey_questions.qid = ' + @tableName + '.id
      AND survey_questions.gid = ' + @tableName + '.token_id
    WHERE survey_questions.sid = ' + surveyId; 


  SET @Sql = query1;        
  PREPARE STMT FROM @Sql; 
  EXECUTE STMT; 
  DEALLOCATE PREPARE STMT;
END