Creating and using functions

You can create user-defined functions in MySQL. These are used to extend the functionality of MySQL, and they work much the same as other built-in functions work. As you may recall, built-in functions are things such as SUM() or AVG().

Understanding the difference between a function and a stored procedure

A function differs from a stored procedure in many ways, as shown in the following table:

Function	Stored procedure
Returns only one mandatory value	Can return zero, one, or multiple values
Doesn't allow transactions	Allow transactions
Can be used in SELECT, WHERE, and HAVING clauses	Can't be used in SELECT, WHERE, and HAVING clauses
Only allows input parameters...