O'Reilly logo

MySQL Stored Procedure Programming by Steven Feuerstein, Guy Harrison

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Stored Functions

Stored functions are similar to stored procedures: they are named program units that contain one or more MySQL statements. They differ from procedures in the following ways:

  • The parameter list of a function may contain only IN parameters. OUT and INOUT parameters are not allowed. Specifying the IN keyword is neither required nor allowed.

  • The function itself must return a single value, whose type is defined in the header of the function.

  • Functions can be called from within SQL statements.

  • A function may not return a result set.

Generally, you should consider using a stored function rather than a stored procedure when you have a program whose sole purpose is to compute and return a single value or when you want to create a user-defined function for use within SQL statements.

Figure 2-16 shows a function that implements the same functionality found in the discount_price stored procedure we created earlier in this chapter.

A stored function
Figure 2-16. A stored function

The following table explains a few things that set apart this function from its stored procedure equivalent:

Line

Explanation

7

Specify a RETURNS clause as part of the function definition. This specifies the type of data that the function will return.

8

MySQL applies stricter rules to stored functions than it does to procedures. A function must either be declared not to modify SQL (using the NO SQL or READS SQL DATA clauses) or be ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required