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

Stored Procedures
317
changes the end-of-statement delimiter from the current value—typically a semicolon
unless you have changed it previously—to a double forward slash.You do this so that you
can use the semicolon delimiter within the stored procedure as you are entering the
code for it without MySQL trying to execute the code as you go.
The next line
create procedure total_orders (out total float)
creates the actual procedure.The name of this procedure is total_orders. It has a single
parameter called total, which is the value you are going to calculate.The word OUT
indicates that this parameter is being passed out or returned.
Parameters can also be declared IN, meaning that a value is being passed into the procedure,
or INOUT, meaning that a value is being passed in but can be changed by the procedure.
The word float indicates the type of the parameter. In this case, you return a total of
all the orders in the orders table.The type of the orders column is float, so the type
returned is also float.The acceptable data types map to the available column types.
If you want more than one parameter, you can provide a comma-separated list of
parameters as you would in PHP.
The body of the procedure is enclosed within the BEGIN and END statements.They are
analogous to the curly braces within PHP ({}) because they delimit a statement block.
In the body, you simply run a SELECT statement.The only difference from normal is
that you include the clause into total to load the result of the query into the total
parameter.
After you have declared the procedure, you return the delimiter back to being a semicolon
with the line
delimiter ;
After the procedure has been declared, you can call it using the call keyword, as
follows:
call total_orders(@t);
This statement calls the total orders and passes in a variable to store the result.To see the
result, you need to then look at the variable:
select @t;
The result should be similar to
+-----------------+
| @t |
+-----------------+
| 289.92001152039 |
+-----------------+
In a way similar to creating a procedure, you can create a function. A function accepts
input parameters (only) and returns a single value.