PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Calculating Dates in PHP
477
Table 21.4
Continued
%e Day of month, numeric, no leading zeros
%m Month, numeric, leading zeros
%c Month, numeric, no leading zeros
%b Month, text, three characters
%j Day of year, numeric
%H Hour, 24-hour clock, leading zeros
%k Hour, 24-hour clock, no leading zeros
%h or %I Hour, 12-hour clock, leading zeros
%l Hour, 12-hour clock, no leading zeros
%i Minutes, numeric, leading zeros
%r Time, 12-hour (hh:mm:ss [AM|PM])
%T Time, 24-hour (hh:mm:ss)
%S or %s Seconds, numeric, leading zeros
%p AM or PM
%w Day of the week, numeric, from 0 (Sunday) to 6 (Saturday)
The UNIX_TIMESTAMP function works similarly but converts a column into a Unix timestamp.
For example,
SELECT UNIX_TIMESTAMP(date_column)
FROM tablename;
returns the date formatted as a Unix timestamp.You can then do as you want with it in
PHP.
You can easily perform date calculations and comparisons with the Unix timestamp.
Bear in mind, however, that a timestamp can usually represent dates only between 1902
and 2038, whereas the MySQL date type has a much wider range.
As a rule of thumb, use a Unix timestamp for date calculations and the standard date
format when you are just storing or showing dates.
Calculating Dates in PHP
A simple way to work out the length of time between two dates in PHP is to use the
difference between Unix timestamps.We use this approach in the script shown in Listing
21.1.
Listing 21.1 calc_age.php—Working Out a Person’s Age Based on Birthdate