Question

我正在创建一个论坛，需要一些反馈。我已经编程了很长时间，但我对MySQL很了解，并且想知道我是否正确地做了这个。

这是我用来输出所选论坛的thr主题索引的查询。我试图在单个查询中收集所有信息，而不是仅收集主题信息，然后在每个循环中收集一次帖子和成员信息，共计35个单独查询（每个查询一个主题）。那是清楚的吗？

基本上，它有效。即使只有300-400个主题，它也有点慢（大约1秒）。

我使用了分析，并收集了最耗时的操作：复制到tmp表：0.538037 发送数据：0.206218 复制到组表：0.137549

编辑：每当有人进入页面时，查询将运行一次（根据站点活动判断，每小时约200-300次）。我打算一次检索大约4000-5000行。

我的问题是：这是最好的方法吗？我可以做些什么来优化这个查询？或者我最好在循环中执行大量较小的查询？

$user_id: id of the user
$forum_id: id of the selected forum


SELECT
  # Topic records
  `topics`.*,

  # First Post
  GROUP_CONCAT(`posts`.`id`) AS `post_id`, # All post ids
  `posts`.`post`    AS `post_first_msg`,
  `posts`.`date`    AS `post_first_date`,
  `posts`.`member`  AS `post_first_member`,

  # First member
  `members`.`id` AS `member_id`,
  `members`.`username` AS member_username,

  # Returns last 3 members' id
  SUBSTRING_INDEX(
    GROUP_CONCAT(`members`.`id` ORDER BY `posts`.`date` DESC SEPARATOR '\\\\'), '\\\\', 3
  ) AS member_last_id,

  # Returns last 3 members' username
  SUBSTRING_INDEX(
    GROUP_CONCAT(`members`.`username` ORDER BY `posts`.`date` DESC SEPARATOR '\\\\'), '\\\\', 3
  ) AS member_last_username,

  # Get last viewed topic id
  `member_topic_lastview`.`lastview` AS `lastview`

FROM
  `topics`

# Returns the `posts` table in ASC order
JOIN (
  SELECT *
  FROM `posts`
  ORDER BY `posts`.`date` ASC
) AS `posts` ON `posts`.`topic` = `topics`.`id`

# Member table, only the columns needed
JOIN (
  SELECT
    `members`.`id`,
    `members`.`username`
FROM `members`
) AS `members` ON `members`.`id` = `posts`.`member`

# Forum table, containing the forum info
LEFT JOIN `forum` ON `forum`.`id` = `topics`.`forum`

# Table containing the latest viewed post id of each topic
LEFT JOIN (
  SELECT *
  FROM `member_topic_lastview`
    WHERE `member_topic_lastview`.`member` = '$user_id'
) AS `member_topic_lastview` ON `member_topic_lastview`.`topic` = `topics`.`id`

WHERE
  `forum` > $forum_id

GROUP BY
  `topics`.`id`

ORDER BY
  `topics`.`sticky` DESC,
  MAX(`posts`.`date`) DESC

LIMIT 35

非常感谢！

Answer 1

首先要做的是查看您的解释计划并发布。另一件突出的事情是你真的不想做很多子查询。

只是为了开始，看看你的第一次加入

FROM
  `topics`

# Returns the `posts` table in ASC order
JOIN (
  SELECT *
  FROM `posts`
  ORDER BY `posts`.`date` ASC
) AS `posts` ON `posts`.`topic` = `topics`.`id`

如果你只是写它，这可能要快得多：

FROM
  `topics`

# Returns the `posts` table in ASC order
JOIN `posts` ON `posts`.`topic` = `topics`.`id`

优化我的MySQL查询

1 个答案: