Question

I have a database like this:

id        User_id    Question_id     Answer
1           john      Question_1        b
2           john      Question_2        a
3           john      Question_3        d
4           harry     Question_1        a
5           harry     Question_2        a  
6           harry     Question_3        c 
7           colleen   Question_1        c
8           colleen   Question_2        a
9           colleen   Question_3        b 

I want to display the content of the above data in the following format-

id     User_id      Question_1      Question_2        Question_3       
1       john             b               a                 d
2       harry            a               a                 c
4       colleen          c               a                 b

How can I achieve this using sql? I am using mysql and php.

Answer 1

SELECT
  id,
  User_id,
  MAX(IF(querstion_id = 'Question_1', answer, NULL)) AS Question_1,
  MAX(IF(querstion_id = 'Question_2', answer, NULL)) AS Question_2,
  MAX(IF(querstion_id = 'Question_3', answer, NULL)) AS Question_3
FROM answers
GROUP BY User_id

EDIT 1
added a php version, see comment

$table = array();
$query = "SELECT * FROM answers ORDER BY User_id, Question_id";

... fetch data depending on what interface you use ...

foreach/while(....)
{
   if(!isset($table[$result['User_id']]))
   {
       $table[$result['User_id']] = array();
       $table[$result['User_id']]['id'] = $result['id'];
       $table[$result['User_id']]['User_id'] = $result['User_id'];
   }

   $table[$result['User_id']][$result['Question_id']] = $result['Answer'];
}

Edit 2 how to display it:

then just display it as you would done with a normal query,
this is how i usaly converts php arrays to html:

echo '<table><thead>';
echo '<tr><th>' . implode('</th><th>', array_keys(current($table))) . '</th></tr>';
echo '</thead><tbody>';
foreach($table as $row)
{
    echo '<tr><td>' . implode('</td><td>', $row) . '</td></tr>';
}
echo '</tbody></table>';