Question

您好我的查询性能有问题，从我看来，group_concat似乎执行得非常慢。事实上，如果我评论它，速度增加上升100倍。无论如何，我可以更改查询，以便它可以更快？这是查询：

redirect_to thanks_subscription_path(@YourSavedObject), notice: 'Some message'

我在想，或许，我可以使用同步的ajax调用来获取group_concat给出的CSV所获得的信息，你认为会更好吗？

以下是EXPLAIN

的结果

SELECT 
      g.id_gara, 
      ( SELECT 
              GROUP_CONCAT( TIG.sigla, (' - '), Cl.sigla, (' ;'), 
              ( SELECT color 
                   FROM bootstrap_colors 
                   where non_color = '0' 
                   ORDER BY RAND() 
                   LIMIT 1 ) ) AS class_sigla 
           FROM 
              associazione_gara_tipologiagara_classifica as A 
                 INNER JOIN tipologie_gare AS TIG 
                    ON A.id_tipologia_gara = TIG.ID 
                 INNER JOIN classifiche_gare AS Cl 
                    ON A.id_classifica = Cl.idclassifiche_gare 
           WHERE 
              A.id_gara = g.id_gara 
           GROUP BY 
              A.id_gara ) cat_class_list,
      tg.bootstrap_description color_gara, 
      ta.bootstrap_description color_aggiudicazione 
   FROM 
      gara g 
         LEFT OUTER JOIN ente AS en 
            ON g.id_ente = en.ID
         LEFT OUTER JOIN tipo_gara AS tg 
            ON g.tipo_gara = tg.idtipo_gara
         LEFT OUTER JOIN admin AS ad 
            ON g.opElab = ad.id
         LEFT OUTER JOIN ente_presso AS ep 
            ON g.indirizzo_ente = ep.idente_presso
         LEFT OUTER JOIN tipo_aggiudicazione_gara AS ta 
            ON g.criterio_aggiudicazione = ta.idtipo_aggiudicazione_gara
   WHERE 
      (en.e_prov LIKE '%bn%') 
   ORDER BY 
      g.id_gara DESC 
   LIMIT 10

Answer 1

碰巧是mysql优化器没有高效执行。它无法轻松解决查询中存在的多个连接。因此，解决此问题的最佳方法是使用SELECT STRAIGHT_JOIN而不是SELECT，以便强制优化器“按原样”执行查询而不尝试优化它。

Saluti。

Group_concat非常慢

1 个答案: