如何编写合并两个记录的函数

Question

我有数据库结构

--car_id 
--from_date_time
--to_date_time
--is_booked

我想这样做：

If any two records having is_booked == 'N" exists in database, having overlapping from_date_time and to_date_time, 
then these records will be merged into a single record.

示例：

If i have records in database like:
Record 1:
from_date_time = '2016-08-01 04:00:00';
to_date_time = '2016-08-01 06:00:00';

Record 2:
from_date_time = '2016-08-01 03:00:00';
to_date_time = '2016-08-01 05:00:00';

Then,above two records will get merged to create following:
from_date_time = '2016-08-01 03:00:00';
to_date_time = '2016-08-01 06:00:00';

我试过以下：

i) Check if the looped_from_date_time is in any database record with from_date_time >= looped_from_date_time  and to_date_time <= looped_from_date_time  and is_booked = "N" and car_id = $car_id.

   iii) Check if the looped_to_date_time is in any database record with from_date_time >= looped_to_date_time and to_date_time <= looped_to_date_time and is_booked = "N" and car_id = $car_id.

但它不起作用

Answer 1

'Period1'与'Period2'重叠

if

NOT ( end_of_period1 < beginning_of_period2 OR 
beginning_of_period1 > end_of_period2). 

这是涵盖所有可能情况的唯一方法。

在你的情况下，我认为第一个条件（I）总是错误的： 如果'from_date_time'在所有记录中始终低于'to_date_time'，则您不能拥有"from_date_time >= looped_from_date_time and to_date_time <= looped_from_date_time"。