You might wonder why anyone would want to use MySQL functions, when PHP comes with a whole bunch of powerful functions of its own. The answer is very simple: the MySQL functions work on the data right there in the database. If you were to use PHP, you would have to extract the raw data from MySQL, manipulate it, and then perform the desired database query.
Using the functions built into MySQL substantially reduces the time needed for performing complex queries, as well as their complexity. If you wish to learn more about the available functions, you can visit the following URLs:
However, to get you started, Appendix D describes a subset of the most useful of these functions.