Christian Roy

I am using Drupal and I changed the way the timezone field is used in the users table. It used to contain the number of seconds difference. For example when my timezone was EST (America/Montreal), then this field would have -18000 as the value.

-5 * 60 * 60 == -18000

Now, this field contains the actual timezone id (America/Montreal or EST). This is much more precise and support daylight savings.

I needed to find all users which their clock is 5AM in order to send them a daily newsletter. But those loving at the other side of the globe would have a different timezone and therefor would get their newsletter at 5PM their time if we sent the newsletter at 5AM Eastern time.

SELECT uid, name, timezone FROM users
WHERE HOUR(CONVERT_TZ(NOW(), @@session.time_zone, IFNULL(timezone, 'GMT'))) = 5;

@@session.time_zone contains the server's timezone for this session.
CONVERT_TZ() converts the given date/time from one timezone to another.

So I am converting the current time from the current timezone to the user's timezone and make sure it's 5 o'clock.