Supporting Features Added in MySQL 5 - Mastering phpMyAdmin 3.4 for Effective MySQL Management - page 293

It might be tempting to open the book table on its Structure page
and look for a list of procedures that manipulate this table, such as
our add_page() procedure. However, all procedures are stored at
the database level, and there is no direct link between the code itself
( UPDATE book ) and the place where the procedure is stored.
Manually creating a function
Functions are similar to stored procedures. However, a function may return just one
value, whereas a stored procedure can have more than one OUT parameter. On the
other hand, using a stored function from within a SELECT statement may seem more
natural as it avoids the need for an intermediate SQL variable to hold the value of an
OUT parameter.
What is the goal of functions? As an example, a function can be used to calculate
the total cost of an order, including tax and shipping. Putting this logic inside the
database instead of at the application level helps to document the application-
database interface. It also avoids duplicating business logic in every application that
needs to deal with this logic.
We should not confuse MySQL 5.0 functions with UDF ( (User-Defined Functions ),
which existed prior to MySQL 5.0. A UDF consists of code written in C or C++,
compiled into a shared object, and referenced with a CREATE FUNCTION statement
and the SONAME keyword.
phpMyAdmin's treatment of functions is, in many ways, similar to what we have
covered in procedures:
• A query box in which to enter a function
• The use of a delimiter
• A mechanism to manipulate a function that is already deined
Let us define a function that retrieves the country name, based on its code. I prefer to
use a param_ prefix to clearly identify the parameters inside the function's definition
and a var_ prefix for local variables. We will use our trusty SQL query box to enter
the function's code, again indicating to this box to use // as the delimiter.
CREATE FUNCTION get_country_name(param_country_code CHAR(2))
RETURNS VARCHAR(50)
READS SQL DATA
BEGIN
DECLARE var_country_name VARCHAR(50) DEFAULT 'not found';
SELECT description