PHP Compare Datetime

I have the following problem. I am trying to compare two datetime values in PHP but the calculation is invalid. There is about 8 hours of difference. I am on my development machine using WAMPServer

if(strtotime($date_time_from_db) < time())
{
    // do something
}

The datetime value in the database is in the following forma开发者_StackOverflow社区t: Y-m-d H:i:s. How can I do this accurately? Also, is using time() a good idea? What happens if the user changes the time on their machine?

Thanks very much!

Don't do date/time comparisons in PHP if you're pulling those values from a database. That involves a double round-trip of conversions: date/time -> text -> date-time. You can do the exact same thing at the database level:

SELECT ...
FROM table
WHERE datetimefield < now()

which allows use of indexes (good) and eliminates two type conversions (also good).

As for user changing time - well, that's just the user's machine. Unless you're doing this as part of an app for sale, then the user has absolutely no way of affecting the time on your database server.