By having functions built into MySQL, the speed of performing complex queries is substantially reduced, as is their complexity. If you wish to learn more about the available functions, you can visit the following URLs:
String functions: http://dev.mysql.com/doc/refman/5.0/en/string-functions.html
Date and time functions: http://dev.mysql.com/doc/refman/5.0/en/date-and-time-functions.html
But, for easy reference, here are some of the most commonly used MySQL functions.