Chapter 6. Date and Time Functions

The ability to record dates and times in a MySQL database is a very common requirement. This chapter presents the date and time functions for MySQL.

Date and time data comprises only numeric strings, so it can be stored in a regular character column. However, by using temporal datatype columns, you can use several built-in functions offered by MySQL. Currently, five temporal datatypes are available: date, time, datetime, timestamp, and year. The date column type is only for recording the date and uses the format yyyy-mm-dd. The time column type is for recording time in the format hhh:mm:ss. To record a combination of date and time, you can use the datetime column type: yyyy-mm-dd hh:mm:ss. The timestamp column is similar to datetime, but is a little limited in its range of allowable time: it starts at the Unix epoch time (i.e., 1970-01-01) and ends at the end of 2037. Finally, the year datatype is used only for recording the year in a column.

Incidentally, any function that calls for a date or a time datatype will also accept a combined datetime datatype. For more information on date and time datatypes, see Appendix A.

Validation of date strings is limited: MySQL makes sure that months range only from 0 to 12, and days range from 0 to 31. Therefore, a date such as February 30 would be accepted. Version 5.0.2 of MySQL will offer more refined validation that would reject such a date.

At the end of this introduction is a listing of date and time functions, grouped by type of function. The bulk of this chapter consists of an alphabetical listing of date and time functions, with explanations of each. Many functions come with examples, along with a resulting display. For help in locating functions, see the index at the back of this book.

For the examples in this chapter, I used the scenario of a professional services firm (e.g., a law firm or an investment advisory firm) that tracks appointments and seminars in MySQL.