为什么我的MySQL查询与多联接如此缓慢？

Question

我想在大约30,000行的表（history_details）上运行一个查询，需要连接几个表（历史记录，房间，室友，属性，listers，学生和管理员）。

1. 第一次加入历史表很简单。
2. 只有满足条件时才应该添加下3个连接（房间，室友，属性）。在这种情况下，它正在查看history_details表中的listing_type列的值是什么，并且如果它是适当的值，则应该将该连接添加到查询中。

3. 之后的3个连接有几个条件需要满足才能包含它们，但在这些条件中可能是任何OR条件。

      SELECT SQL_CALC_FOUND_ROWS 
           history_details.history_id, 
           history_details.listing_type, 
           history_details.listing_id, 
           history_details.date_added, 
           history_details.field, 
           history_details.before_value, 
           history_details.after_value, 
           history_details.edit_group, 
           history_details.email, 
           history_details.name, 
           history_details.correction_message, 
           history_details.photo_filepath, 
           history.history_message, 
           listers.first_name, 
           listers.last_name, 
           students.first_name, 
           students.last_name, 
           admin.first_name, 
           admin.last_name 
          FROM history_details 
          LEFT JOIN history 
           ON history_details.history_id = history.history_id 
          LEFT JOIN rooms 
           ON history_details.listing_type="room" AND rooms.room_id = history_details.listing_id 
          LEFT JOIN roommates 
           ON history_details.listing_type="roommate" 
           AND roommates.roommate_id = history_details.listing_id 
          LEFT JOIN properties 
           ON history_details.listing_type="property" 
           AND properties.property_id = history_details.listing_id 
          LEFT JOIN listers 
           ON (history_details.listing_type="lister" AND listers.lister_id = history_details.listing_id) 
           OR (history_details.listing_type="property" AND listers.lister_id = properties.lister_id) 
           OR (history_details.listing_type="room" AND rooms.lister_type="lister" AND listers.lister_id = rooms.lister_id) 
          LEFT JOIN students 
           ON (history_details.listing_type="student" AND students.student_id = history_details.listing_id) 
           OR (history_details.listing_type="roommate" AND students.student_id = roommates.student_id) 
           OR (history_details.listing_type="room" AND rooms.lister_type="student" AND students.student_id = rooms.lister_id) 
          LEFT JOIN admin 
           ON history_details.listing_type="admin" AND admin.admin_id = history_details.listing_id 
          LIMIT 0,100 
   

它给我正确的结果，但它正在73秒运行。我添加了索引，但我不确定它们是否被使用。这是它显示了当我运行使用EXPLAIN SELECT SQL_CALC_FOUND_ROWS ....

这是它显示了当我运行使用EXPLAIN SELECT ....

这是我加入的各种表的索引解释说明： history_details

PR operties

客房

室友

你能告诉我，如果正在使用我的索引？另外，如何改进查询，表格结构或索引以提高速度？

编辑： 感谢阿马丹的有益建议，它现在运行在147ms而不是73秒之前。这是最终的查询我最终使用：

   SELECT SQL_CALC_FOUND_ROWS 
        history_details.*, 
        listers.first_name AS lister_first_name, 
        listers.last_name AS lister_last_name, 
        NULL AS student_first_name, 
        NULL AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN listers 
        ON listers.lister_id = history_details.listing_id 
       WHERE history_details.listing_type="lister" 

       UNION 

       SELECT history_details.*, 
        NULL AS lister_first_name, 
        NULL AS lister_last_name, 
        students.first_name AS student_first_name, 
        students.last_name AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN students 
        ON students.student_id = history_details.listing_id 
       WHERE history_details.listing_type="student" 

       UNION 

       SELECT history_details.*, 
        listers.first_name AS lister_first_name, 
        listers.last_name AS lister_last_name, 
        NULL AS student_first_name, 
        NULL AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN properties 
        ON properties.property_id = history_details.listing_id 
       LEFT JOIN listers 
        ON listers.lister_id = properties.lister_id 
       WHERE history_details.listing_type="property" 

       UNION 

       SELECT history_details.*, 
        listers.first_name AS lister_first_name, 
        listers.last_name AS lister_last_name, 
        students.first_name AS student_first_name, 
        students.last_name AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN rooms 
        ON rooms.room_id = history_details.listing_id 
       LEFT JOIN listers 
        ON (rooms.lister_type="lister" AND listers.lister_id = rooms.lister_id) 
       LEFT JOIN students 
        ON (rooms.lister_type="student" AND students.student_id = rooms.lister_id) 
       WHERE history_details.listing_type="room" 

       UNION 

       SELECT history_details.*, 
        NULL AS lister_first_name, 
        NULL AS lister_last_name, 
        students.first_name AS student_first_name, 
        students.last_name AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN roommates 
        ON roommates.roommate_id = history_details.listing_id 
       LEFT JOIN students 
        ON students.student_id = roommates.student_id 
       WHERE history_details.listing_type="roommate" 

       UNION 

       SELECT history_details.*, 
        NULL AS lister_first_name, 
        NULL AS lister_last_name, 
        NULL AS student_first_name, 
        NULL AS student_last_name, 
        admin.first_name AS admin_first_name, 
        admin.last_name AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN admin 
        ON admin.admin_id = history_details.listing_id 
       WHERE history_details.listing_type="admin" 
       ORDER BY history_details_id DESC 
       LIMIT 0,100 

Answer 1

其中key是NULL中的行，所以不能用这些表的任何索引。即listers和students未被优化。那是因为它的索引是不可能的，因为你使用OR来产生它。做几个查询，其中每个history_details.listing_type和UNION他们。是的，它看起来很丑，这是很多重复，但速度会在那里。

联盟语法如下：

SELECT ... 
WHERE history_details.listing_type="lister" 
UNION 
SELECT ... 
WHERE history_details.listing_type="property" 
UNION 
SELECT ... 
WHERE history_details.listing_type="room" 
UNION 
SELECT ... 
WHERE history_details.listing_type="admin" 
.... 
... 
ORDER BY whatever 
LIMIT whatever, whatever 

确保每个SELECT具有字段（这样你才会有无用加入做就算了，但他们会很快，因为它们会被索引的数量相等）。 ...基本上是您的整个查询（SELECT field1, field2... FROM table1 LEFT JOIN table2 ON condition ...），但OR取出lister和student条款。 UNION将组合所有子选择的行。 ORDER和LIMIT将适用于工会的结果，而不是最后的SELECT。