Title:PHP and the MySQL datetime data type
Author:Mark Kiehl
Category:PHP
MySQL datetime

Setup MySQL table with field/column `last_datetime` as follows:
Type: timestamp
Attributes: ON UPDATE CURRENT_TIMESTAMP
Null: not null
Default: CURRENT_TIMESTAMP

Whenever the table is updated (UPDATE query), the field `last_datetime` is automatically updated.
To get the records within a specified period of time (20 min), execute a select query as follows:

SELECT timestampdiff(minute,`last_datetime`,now()) as `elapsedMin` FROM `tableName` WHERE timestampdiff(minute,`last_datetime`,now())<'20'