MySQL查询优化JOIN
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;
在c.id_apps，a.id_apps，c.id_utilisateur，u.id_utilisateur和c.date_commentaire上有一个MySQL INDEX。
解释结果：
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;
解释结果：
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 |
在a.categorie上有一个MySQL INDEX，c.id_cat，a.editeur，e.id_edit和a.id_apps
谢谢
谢谢你们，对不起马塞洛这是我第一次在Stackoverflow上
带有EXPLAIN的第一个查询：
id select_type表类型possible_keys key key_len ref行额外
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
第二个
id select_type表类型possible_keys key key_len ref行额外
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