Question

我想让我的Flarum论坛在手动干预数据库后更新其讨论记录。（Flarum仍然处于测试阶段且仍然缺少许多功能，因此手动修复这些事情并不常见。）我设法编写了以下查询，它可以完成我想要的工作：

UPDATE discussions as d SET
  d.start_time =
    (SELECT min(p.time) FROM posts as p
         WHERE p.discussion_id = d.id),
  d.last_time =
    (SELECT max(p.time) FROM posts as p
         WHERE p.discussion_id = d.id),
  d.comments_count =
    (SELECT count(*) FROM posts as p
         WHERE p.discussion_id = d.id AND p.type = 'comment'),
  d.participants_count =
    (SELECT count(DISTINCT p.user_id) FROM posts as p
         WHERE p.discussion_id = d.id),
  d.start_post_id =
    (SELECT p.id FROM posts as p
         WHERE p.discussion_id = d.id
         ORDER BY p.number ASC LIMIT 1),
  d.start_user_id =
    (SELECT p.user_id FROM posts as p
         WHERE p.discussion_id = d.id
         ORDER BY p.number ASC LIMIT 1),
  d.last_post_id =
    (SELECT p.id FROM posts as p
         WHERE p.discussion_id = d.id
         ORDER BY p.number DESC LIMIT 1),
  d.last_post_number =
    (SELECT p.number FROM posts as p
         WHERE p.discussion_id = d.id
         ORDER BY p.number DESC LIMIT 1),
  d.last_user_id =
    (SELECT p.user_id FROM posts as p
         WHERE p.discussion_id = d.id
         ORDER BY p.number DESC LIMIT 1);

但它看起来很难看。我确信有一种方法可以更简洁有效的方式编写相同的逻辑，但我并不是真的想知道如何做到这一点。有人能告诉我如何消除这些几乎重复的子查询吗？

上面提到的表定义如下（省略了一些细节）：

CREATE TABLE discussions (
  id                   int unsigned NOT NULL AUTO_INCREMENT,
  title                varchar(200) NOT NULL,
  comments_count       int(10) unsigned NOT NULL DEFAULT '0',
  participants_count   int(10) unsigned NOT NULL DEFAULT '0',
  number_index         int(10) unsigned NOT NULL DEFAULT '0',
  start_time           datetime NOT NULL,
  start_user_id        int(10) unsigned DEFAULT NULL,
  start_post_id        int(10) unsigned DEFAULT NULL,
  last_time            datetime DEFAULT NULL,
  last_user_id         int(10) unsigned DEFAULT NULL,
  last_post_id         int(10) unsigned DEFAULT NULL,
  last_post_number     int(10) unsigned DEFAULT NULL,
  ... );

CREATE TABLE posts (
  id                   int(10) unsigned NOT NULL AUTO_INCREMENT,
  discussion_id        int(10) unsigned NOT NULL,
  number               int(10) unsigned DEFAULT NULL,
  time                 datetime NOT NULL,
  user_id              int(10) unsigned DEFAULT NULL,
  type                 varchar(100) DEFAULT NULL,
  ... );

Flarum使用MySQL作为其主要存储后端，因此特定于MySQL的解决方案会很好。但是，如果有人知道如何在ANSI-SQL中解决问题，那将会很棒。

Answer 1

你可以使用内连接并使用max和min作为第一个和最后一个

{"multicast_id":8241088978207626504,"success":0,"failure":1,"canonical_ids":0,"results":[{"error":"InvalidRegistration"}]} 0 .

在UPDATE语句中简化多个子查询

1 个答案: