title: What does "using join buffer" means in the Explain table of an MySQL query?
body: <p>I have the following complex query and I notice that it is making my website so slow I want to find a way to optimize it:</p>
  
  <pre><code>SELECT tahminler.result,
  tahminler.tahmin,
  tahminler.match_id, 
  tahminler.timestamp, 
  tahminler.tahmin_text, 
  users.username, 
  matches_of_comments.tournament_id,
  matches_of_comments.match_status,
  matches_of_comments.match_date,
  matches_of_comments.localteam_name,
  matches_of_comments.visitorteam_name,
  matches_of_comments.localteam_id,
  matches_of_comments.visitorteam_id,
  matches_of_comments.localteam_goals,
  matches_of_comments.visitorteam_goals,
  new_iddaa.iddaa_code, 
  tahminler_results.ms1, 
  tahminler_results.ms2, 
  tahminler_results.ms0, 
  tahminler_results.alt, 
  tahminler_results.ust, 
  tahminler_results.tg_0_1, 
  tahminler_results.tg_2_3, 
  tahminler_results.tg_4_6, 
  tahminler_results.tg_7, 
  tahminler_results.kg_var, 
  tahminler_results.kg_yok, 
  tahmins.tahmin as text_tahmin 
  FROM tahminler 
  INNER JOIN users on users.id = tahminler.user_id 
  INNER JOIN matches_of_comments on tahminler.match_id = matches_of_comments.match_id 
  Left JOIN new_iddaa on new_iddaa.match_id = matches_of_comments.match_id 
  INNER JOIN tahmins on tahminler.tahmin = tahmins.id 
  LEFT JOIN tahminler_results on tahminler.match_id = tahminler_results.match_id 
  Where tahminler.user_id = $user_id 
  order by tahminler.timestamp DESC
  </code></pre>
  
  <p>I do not have much experience in databases or optimization so I did an Explain for this query and i got this table :</p>
  
  <p><img src="https://i.stack.imgur.com/nHvlt.png" alt="explain table"></p>
  
  <p>I think the problem in the row which tells "using join buffer" but what does that mean ??
  can you help me to understand this point and making the query optimized ?</p>