mysql - group_concat 非常慢

Question

您好，我的查询性能存在问题，据我所知，group_concat 似乎执行速度非常慢。事实上，如果我评论它，速度增益会提高 100 倍。无论如何，我可以更改查询以使其更快吗？这是查询:

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

我在想，或者，我可以使用同步的 ajax 调用来获取通过 group_concat 给出的 CSV 获得的信息，您认为这样会更好吗？

这是 EXPLAIN 的结果

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra
1   PRIMARY     en  ALL     PRIMARY     NULL    NULL    NULL    12889   Using where; Using temporary; Using filesort
1   PRIMARY     g   ref     id_ente     id_ente     5   disasrl.en.ID   4   NULL
1   PRIMARY     tg  eq_ref  PRIMARY     PRIMARY     4   disasrl.g.tipo_gara     1   NULL
1   PRIMARY     ad  eq_ref  PRIMARY,id  PRIMARY     4   disasrl.g.opElab    1   Using index
1   PRIMARY     ep  eq_ref  PRIMARY     PRIMARY     4   disasrl.g.indirizzo_ente    1   Using index
1   PRIMARY     ta  eq_ref  PRIMARY     PRIMARY     4   disasrl.g.criterio_aggiudicazione   1   NULL
2   DEPENDENT SUBQUERY  A   ALL     NULL    NULL    NULL    NULL    152721  Using where; Using filesort
2   DEPENDENT SUBQUERY  Cl  eq_ref  PRIMARY     PRIMARY     4   disasrl.A.id_classifica     1   NULL
2   DEPENDENT SUBQUERY  TIG     eq_ref  PRIMARY     PRIMARY     4   disasrl.A.id_tipologia_gara     1   NULL
3   UNCACHEABLE SUBQUERY    bootstrap_colors    ALL     NULL    NULL    NULL    NULL    11  Using where; Using temporary; Using filesort

Answer 1

恰好是 mysql 优化器没有高效执行。它无法轻松解析查询中存在的许多联接。因此，解决此问题的最佳方法是使用 SELECT STRAIGHT_JOIN 而不仅仅是 SELECT，以便强制优化器“按原样”执行查询而不尝试优化它。

敬礼。