检查表的时间重叠?

问题描述

我有一个包含以下字段的 MySQL 表:

I have a MySQL table with the following fields:

• 姓名
• 开始时间
• 结束时间

starttime 和 endtime 是 MySQL TIME 字段(不是 DATETIME).我需要一种方法来定期扫描"表格以查看表格内的时间范围是否有任何重叠.如果有一个来自 10:00-11:00 的事件和另一个来自 10:30-11:30 的事件，我想收到时间重叠的警报.

starttime and endtime are MySQL TIME fields (not DATETIME). I need a way to periodically "scan" the table to see if there are any overlaps in time ranges within the table. If there is an event from 10:00-11:00 and another from 10:30-11:30, I want to be alerted of the presence of the time overlap.

没什么特别的，我只想知道是否存在重叠.

Nothing fancy really, all I want to know whether an overlap exists or not.

我将使用 PHP 来执行此操作.

I'm going to be using PHP to execute this.

推荐答案

这是一个我多年前找到答案的查询模式:

This is a query pattern for which I found the answer many years ago:

SELECT *
FROM mytable a
JOIN mytable b on a.starttime <= b.endtime
    and a.endtime >= b.starttime
    and a.name != b.name; -- ideally, this would compare a "key" column, eg id

要找到任何重叠"，您可以将时间范围的相反两端相互比较.我不得不拿出笔和纸来绘制相邻的范围，才能意识到边缘情况归结为这种比较.

To find "any overlap", you compare the opposite ends of the timeframe with each other. It's something I had to get a pen and paper out for and draw adjacent ranges to realise that the edge cases boiled down to this comparison.

如果您想防止任何行重叠，请将此查询的变体放入触发器中:

If you want to prevent any rows from overlapping, put a variant of this query in a trigger:

create trigger mytable_no_overlap
before insert on mytable
for each row
begin
  if exists (select * from mytable
             where starttime <= new.endtime
             and endtime >= new.starttime) then
    signal sqlstate '45000' SET MESSAGE_TEXT = 'Overlaps with existing data';
  end if;
end;

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