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

320 Chapter 13 Advanced MySQL Programming
Listing 13.4
Continued
create procedure largest_order(out largest_id int)
begin
declare this_id int;
declare this_amount float;
declare l_amount float default 0.0;
declare l_id int;
declare done int default 0;
declare continue handler for sqlstate '02000' set done = 1;
declare c1 cursor for select orderid, amount from orders;
open c1;
repeat
fetch c1 into this_id, this_amount;
if not done then
if this_amount > l_amount then
set l_amount=this_amount;
set l_id=this_id;
end if;
end if;
until done end repeat;
close c1;
set largest_id=l_id;
end
//
delimiter ;
This code uses control structures (both conditional and looping), cursors, and declare
handlers. Let’s consider it line by line.
At the start of the procedure, you declare a number of local variables for use within
the procedure.The variables this_id and this_amount store the values of orderid and
amount in the current row.The variables l_amount and l_id are for storing the largest
order amount and the corresponding ID. Because you will work out the largest amount
by comparing each value to the current largest value, you initialize this variable to zero.
The next variable declared is done, initialized to zero (false).This variable is your
loop flag.When you run out of rows to look at, you set this variable to 1 (true):
The line
declare continue handler for sqlstate ‘02000’ set done = 1;
is called a declare handler. It is similar to an exception in stored procedures. Also available
are continue handlers and exit handlers. Continue handlers, like the one shown, take the