如何检查mysql中两个日期范围是否重叠？

Question

在mysql中,如何检查两个日期范围是否重叠？

我有这个:

注意:我们有,p.date_started <= p.date_finished但dateA可以等于dateB或小于dateB或大于dateB.

码:

    $query = "SELECT u.first_name, u.last_name, u.avatar_filename, p.id, p.user_id, p.address, p.topic, p.latitude, p.longitude, d.name AS department_name
              FROM user u
              JOIN placement p ON p.user_id=u.id
              JOIN department d ON d.id = u.department_id
              WHERE p.active=1 AND (('{$dateA}' BETWEEN p.date_started AND p.date_finished) OR 
                                    ('{$dateB}' BETWEEN p.date_started AND p.date_finished) OR
                                    (p.date_started BETWEEN '{$dateA}' AND '{$dateB}') OR
                                    (p.date_finished BETWEEN '{$dateA}' AND '{$dateB}'))";

有没有更好的方法呢？

谢谢

Answer 1

如果我们保证date_started,datefinished,$DateA和$DateB不为NULL,并且我们保证date_started不大于date_finished...

`s` represents `date_started`
`f` represents `date_finished`
`a` represents the smaller of `$DateA` and `$DateB`
`b` represents the larger of `$DateA` and `$DateB`

视觉:

      s-----f       overlap
 -----+-----+-----  -------  
  a-b |     |        NO
  a---b     |        YES
  a-----b   |        YES
  a---------b        YES
  a-----------b      YES
      a---b |        YES
      a-----b        YES
      a-------b      YES
      | a-b |        YES
      | a---b        YES     
      | a-----b      YES     
      |     a-b      YES
      |     | a-b    NO

我们可以很容易地检测到范围没有"重叠"的时间:

( a > f OR b < s )

我们可以轻易地否定,要返回"真"时,有是一个"重叠":

NOT ( a > f OR b < s )

将其转换为SQL:

NOT ( GREATEST('{$dateA}','{$dateB}') < p.date_started
      OR LEAST('{$dateA}','{$dateB}') > p.date_finished
    )