优化复杂的mysql查询

Question

以下查询在phpmyadmin上花费0.1313秒。 有什么方法可以优化它，从而使事情更快（比如说在0.00XX秒内得到它）？ 已经在进行联接的列上添加了索引。

SELECT m.id, m.civ, m.prenom, m.nom, m.sexe, m.depart, m.date_entree, m.date_sortie, m.login_userid, m.login_passwd, a.rank_id, r.rank_m, r.rank_f, d.user_id AS depID, c.nom AS cordo, z.rank
FROM `0_member` AS m
LEFT JOIN `0_area` AS a ON ( m.id = a.user_id
AND a.sec_id =2 )
LEFT JOIN `0_rank` AS r ON r.id = a.rank_id
LEFT JOIN `0_depart` AS d ON ( m.depart = d.depart
AND d.user_sec =2 )
LEFT JOIN `0_area` AS z ON ( d.user_id = z.user_id
AND z.sec_id =2 )
LEFT JOIN `0_member` AS c ON d.user_id = c.id
WHERE z.rank = 'mod'
ORDER BY nom

Answer 1

您的查询在别名为“ Z”的“ Z”别名表中的FOUND值上具有最终的“ WHERE”子句，但查询为所有LEFT JOIN，表示您希望所有成员，无论右侧是否可能匹配您要加入的表。

此外，您通过离开并离开用户ID来下游连接到“ z”表，然后直接作为用户ID上的A表直接重新连接到“ 0_area”，这看起来与从用户ID中找到的相同无论如何，将离开表链接到“ z”表。

也就是说，您的成员加入后出发，然后前往该地区...

我的建议（并且我可以这样重写查询）是颠倒查询的顺序，将您的Area表放在FIRST上，并在“ sec_id，rank”上建立索引...我将根据任何类别获得关键顺序首先具有较小的子集列...因此是SEC_ID，RANK或RANK，SEC_ID。 然后对其他表进行简单的JOIN（而不是LEFT JOIN）操作...至少从：

SELECT STRAIGHT_JOIN
      m.id, 
      m.civ, 
      m.prenom, 
      m.nom, 
      m.sexe, 
      m.depart,  
      m.date_entree, 
      m.date_sortie, 
      m.login_userid, 
      m.login_passwd, 
      a.rank_id, 
      r.rank_m, 
      r.rank_f, 
      d.user_id AS depID, 
      c.nom AS cordo, 
      z.rank
   FROM 
      `0_area` AS z
          JOIN `0_depart` AS d
             on z.user_id = d.user_id
             and d.user_sec = 2
             JOIN `0_member` AS m
                on d.depart = m.depart
                AND z.user_id = m.id
          LEFT JOIN `0_rank` AS r
             on z.rank_id = .rid
   WHERE
          z.sec_id = 2
      AND z.rank = 'mod'
   ORDER BY
      nom

在原始查询中，您来自

member
   Links to Area (on member's user ID just to ensure the "sec_id = 2")

由于新查询专门以“ area”表作为“ Z”别名开头，并且THAT where子句显式为“ sec_id = 2”值，因此您无需再进行反向链接...

Area (only SECID = 2 and rank = mod)
  Links to Depart (on the User's ID)
      Links to Members by (on the depart ID)

Answer 2

像使用“ z.rank ='mod'”一样，尝试将此语句“ a.sec_id = 2”，“ d.user_sec = 2”，“ z.sec_id = 2”从ON部分移动到WHERE部分。 像这样：

SELECT m.id, m.civ, m.prenom, m.nom, m.sexe, m.depart, m.date_entree, m.date_sortie, m.login_userid, m.login_passwd, a.rank_id, r.rank_m, r.rank_f, d.user_id AS depID, c.nom AS cordo, z.rank
FROM `0_member` AS m
LEFT JOIN `0_area` AS a ON m.id = a.user_id
LEFT JOIN `0_rank` AS r ON r.id = a.rank_id
LEFT JOIN `0_depart` AS d ON m.depart = d.depart
LEFT JOIN `0_area` AS z ON d.user_id = z.user_id
LEFT JOIN `0_member` AS c ON d.user_id = c.id
WHERE z.rank = 'mod'
AND a.sec_id =2
AND d.user_sec =2
AND z.sec_id =2
ORDER BY nom