Question

我正在尝试在一个包含大约30,000行的表（history_details）上运行查询，并且需要连接多个表（历史记录，房间，室友，属性，列表，学生和管理员）。

第一次加入历史记录表非常简单。
只有满足条件才能添加下3个连接（房间，室友，属性）。在这种情况下，它查看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。

接下来的3个连接有几个条件需要满足才能包含它们，但在这种情况下它可能是任何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

它给了我正确的结果，但它需要73秒才能运行。我添加了索引，但我不确定它们是否被使用。这是我使用EXPLAIN SELECT SQL_CALC_FOUND_ROWS ....

enter image description here

这是我使用EXPLAIN SELECT ....运行Explain时显示的内容 enter image description here

这些是我添加到各种表中的索引：的 history_details enter image description here

属性 enter image description here

间 enter image description here

室友 enter image description here

你能告诉我我的索引是否被使用？另外，如何改进查询，表结构或索引以提高速度？

修改感谢Amadan的有用建议，它现在以147毫秒而不是73秒运行。这是我最终使用的最终查询：

                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

key为NULL的行，它不使用这些表的任何索引。即listers和students未被优化。这是因为它上面的索引是不可能的，因为你使用OR来生成它。进行多次查询，每次history_details.listing_type一次，UNION次。是的，它看起来很丑陋，重复很多，但速度会很快。

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具有相同数量的字段（因此您甚至必须执行无用的连接，但它们将很快，因为它们将被编入索引）。 ...基本上是您的整个查询（SELECT field1, field2... FROM table1 LEFT JOIN table2 ON condition ...），但从OR和lister条款中取出student。 UNION将组合子选择的所有行。 ORDER和LIMIT将适用于结合的结果，而不是最后的SELECT。

为什么我的MySQL连接查询速度如此之慢？

1 个答案: