title: Multiple LEFT JOIN in multiple tables
body: <p>I have the following SQL select:</p>
  
  <pre><code>SELECT s.*,
         GROUP_CONCAT(CONCAT_WS(':', m.type, m.id, m.filename) SEPARATOR ',') AS multimedia,
         GROUP_CONCAT(CONCAT_WS(':', c.id) SEPARATOR ',') AS categories
  FROM sections s 
  
  
  LEFT JOIN sections_multimedia sm
       ON s.id = sm.section_id 
  LEFT JOIN multimedia m
       ON sm.multimedia_id = m.id 
  
  
  LEFT JOIN sections_categories sc
       ON s.id = sc.section_id 
  LEFT JOIN categories c
       ON sc.category_id = c.id
  
  
  WHERE s.id = s.id
  GROUP BY s.id
  ORDER BY s.position, s.id ASC;
  </code></pre>
  
  <p>As a result, the field 'categories' has the correct values, which are(2,3), but unfortunately repeated many times! (the result is: 2,2,2,2,2,2,3,3,3,3,3,3)</p>
  
  <p>What is wrong with my select?</p>
  
  <p>Thank you for your replies!</p>