In this hour, you learned how to use various PHP functions to perform date- and time-related actions. The time() function gets a date stamp for the current date and time, and you can use getdate() to extract date information from a timestamp and date() to convert a timestamp into a formatted string. You learned how to create a timestamp using mktime(), and how to test a date for validity with checkdate().
Additionally, you discovered that MySQL's built-in date and time functions can definitely take some of the load off your application by internally formatting dates and times and performing the date and time arithmetic. The formatting options used for the DATE_FORMAT() function provide a simple method to produce a custom display string from any sort of date field. The DATE_ADD() and DATE_SUB() functions and their numerous available interval types help you determine dates and times in the past or future. Additionally, functions such as DAY(), WEEK(), MONTH(), and YEAR() are useful for extracting parts of dates for use in WHERE or ORDER BY clauses.