Question

SELECT submissions.created_at, guests.accepted
FROM submission
INNER JOIN guests
ON guests.event_id = 1
ORDER BY submissions.created_at ASC;

目前此查询需要很长时间才能运行（甚至可能无法返回所有内容）。我想要完成的任务：

抓取字段submissions.created at和guests.accepted（两者通过submission_id链接）给定某个event_id（例如事件1）。

我的查询有什么问题？

Answer 1

您忘记在查询中提供JOIN条件。试试这个：

SELECT submissions.created_at, guests.accepted
FROM submission s
INNER JOIN guests g on g.event_id = s.submissions_id
where guests.event_id = 1
ORDER BY submissions.created_at ASC;

Answer 2

SELECT submissions.created_at, guests.accepted
FROM submission
INNER JOIN guests
ON guests.(column to match against) = submissions.(column to match on)
where guests.event_id=1
ORDER BY submissions.created_at ASC;

正如这里的许多其他人已经说过的那样，你的加入有点蠢。它正在尝试将来宾表中匹配的一行与提交列中的每一行连接起来。

Answer 3

您需要像这样进行加入：

Inner join guest on guest.event_id = submissions_id
where guest.event_id = 1

当你加入时，你需要加入来自不同表的两列（大多数时候是id列）您可以阅读MySQL example以获取更多解释。以下是MySQL reference manual

的链接

查询效率低下

3 个答案: