MySQL查询优化JOIN

Question

我需要你的帮助来优化那些mysql查询，两者都在我的慢速查询日志中。

SELECT a.nom, c.id_apps, c.id_commentaire, c.id_utilisateur, 
     c.note_commentaire, u.nom_utilisateur 
    FROM comments AS c 
    LEFT JOIN apps AS a ON c.id_apps = a.id_apps 
    LEFT JOIN users AS u ON c.id_utilisateur = u.id_utilisateur 
ORDER BY c.date_commentaire DESC LIMIT 5; 

有上c.id_apps，a.id_apps，c.id_utilisateur，u.id_utilisateur和c.date_commentaire一个MySQL索引。

EXPLAIN结果：

 
id | select_type | table | type | possible_keys | key    | key_len | ref    | rows | Extra 
1 | SIMPLE  | c | index | NULL   | date_commentaire | 8  | NULL    | 119 | 
1 | SIMPLE  | a | eq_ref | PRIMARY  | PRIMARY   | 3  | c.id_apps  | 1 | 
1 | SIMPLE  | u | eq_ref | PRIMARY  | PRIMARY   | 3  | c.id_utilisateur | 1 | 

---

SELECT a.id_apps, a.id_itunes, a.nom, a.prix, a.resume, c.nom_fr_cat, e.nom_edit 
    FROM apps AS a 
    LEFT JOIN cat AS c ON a.categorie = c.id_cat 
    LEFT JOIN edit AS e ON a.editeur = e.id_edit 
ORDER BY a.id_apps DESC LIMIT 20; 

EXPLAIN结果：

 
id | select_type | table | type | possible_keys | key | key_len | ref   | rows | Extra 
1 | SIMPLE  | a | index | NULL   | PRIMARY | 3 | NULL  | 5336 | 
1 | SIMPLE  | c | eq_ref | PRIMARY  | PRIMARY | 1 | a.categorie | 1 | 
1 | SIMPLE  | e | eq_ref | PRIMARY  | PRIMARY | 3 | a.editeur | 1 |

有上a.categorie，c.id_cat，a.editeur，E中的MySQL索引的。 id_edit and a.id_apps

谢谢

Answer 1

谢谢你们&对不起马塞洛这是我第一次＃2

与第一查询说明：

ID SELECT_TYPE表类型possible_keys关键key_len裁判行额外

1简单的C指数NULL date_commentaire 8 NULL 119
1 SIMPLE一个eq_ref PRIMARY PRIMARY 3个c.id_apps 1
1简单U eq_ref PRIMARY PRIMARY 3 c.id_utilisateur 1

而第二

ID SELECT_TYPE表型possible_keys键key_len REF行额外

1 SIMPLE一个索引NULL PRIMARY 3 NULL 5336
1简单的C eq_ref PRIMARY PRIMARY 1 a.categorie 1
1简单的电子eq_ref PRIMARY PRIMARY 3 a.editeur 1