PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

316 Chapter 13 Advanced MySQL Programming
You can also make these changes to the existing table using ALTER TABLE statements,
as follows:
alter table order_items type=InnoDB;
alter table order_items
add foreign key (orderid) references orders(orderid);
To see that this change has worked, you can try to insert a row with an orderid for
which there is no matching row in the orders table:
insert into order_items values (77, '0-672-31697-8', 7);
You should receive an error similar to
ERROR 1452 (23000): Cannot add or update a child row:
a foreign key constraint fails
Stored Procedures
A stored procedure is a programmatic function that is created and stored within
MySQL. It can consist of SQL statements and a number of special control structures. It
can be useful when you want to perform the same function from different applications
or platforms, or as a way of encapsulating functionality. Stored procedures in a database
can be seen as analogous to an object-oriented approach in programming.They allow
you to control the way data is accessed.
Let’s begin by looking at a simple example.
Basic Example
Listing 13.1 shows the declaration of a stored procedure.
Listing 13.1
basic_stored_procedure.sql—Declaring a Stored Procedure
# Basic stored procedure example
delimiter //
create procedure total_orders (out total float)
BEGIN
select sum(amount) into total from orders;
END
//
delimiter ;
Let’s go through this code line by line.
The first statement
delimiter //