Summary: in this tutorial, you will learn how to write MySQL stored procedures that have parameters. You will also go through a couple of stored procedure examples to understand different kinds of parameters.
Introduction to MySQL stored procedure parameters
Almost stored procedures that you develop require parameters. The parameters make the stored procedure more flexible and useful. In MySQL, a parameter has one of three modes:
IN– is the default mode. When you define an
INparameter in a stored procedure, the calling program has to pass an argument to the stored procedure. In addition, the value of an
INparameter is protected. It means that even the value of the
INparameter is changed inside the stored procedure, its original value is retained after the stored procedure ends. In other words, the stored procedure only works on the copy of the
OUT– the value of an
OUTparameter can be changed inside the stored procedure and its new value is passed back to the calling program. Notice that the stored procedure cannot access the initial value of the
OUTparameter when it starts.
INOUTparameter is the combination of
OUTparameters. It means that the calling program may pass the argument, and the stored procedure can modify the
INOUTparameter and pass the new value back to the calling program.
The syntax of defining a parameter in the stored procedures is as follows:
MODE param_name param_type(param_size)
INOUT, depending on the purpose of the parameter in the stored procedure.
param_nameis the name of the parameter. The name of the parameter must follow the naming rules of the column name in MySQL.
- Followed the parameter name is its data type and size. Like a variable, the data type of the parameter can be any valid MySQL data type.
Each parameter is separated by a comma (
,) if the stored procedure has more than one parameter.
Let’s practice with some examples to get a better understanding. We will use the tables in the sample database for the demonstration.
MySQL stored procedure parameter examples
The IN parameter example
The following example illustrates how to use the
IN parameter in the
GetOfficeByCountry stored procedure that selects offices located in a particular country.
CREATE PROCEDURE GetOfficeByCountry(IN countryName VARCHAR(255))
WHERE country = countryName;
countryName is the
IN parameter of the stored procedure. Inside the stored procedure, we select all offices that locate in the country specified by the
Suppose, we want to get all offices in the USA, we just need to pass a value (USA) to the stored procedure as follows:
To get all offices in France, we pass the France literal string to the
GetOfficeByCountry stored procedure as follows:
The OUT parameter example
The following stored procedure returns the number of orders by order status. It has two parameters:
INparameter that is the order status which we want to count the orders.
OUTparameter that stores the number of orders for a specific order status.
The following is the source code of the
CountOrderByStatus stored procedure.
CREATE PROCEDURE CountOrderByStatus(
IN orderStatus VARCHAR(25),
OUT total INT)
WHERE status = orderStatus;
To get the number of shipped orders, we call the
CountOrderByStatus stored procedure and pass the order status as
Shipped, and also pass an argument (
@total ) to get the return value.
To get the number of orders that are in process, we call the
CountOrderByStatus stored procedure as follows:
CALL CountOrderByStatus('in process',@total);
SELECT @total AS total_in_process;
The INOUT parameter example
The following example demonstrates how to use an
INOUT parameter in the stored procedure.
CREATE PROCEDURE set_counter(INOUT count INT(4),IN inc INT(4))
SET count = count + inc;
How it works.
set_counterstored procedure accepts one
count) and one
- Inside the stored procedure, we increase the counter (
count) by the value of the
See how we call the
set_counter stored procedure:
SET @counter = 1;
CALL set_counter(@counter,1); -- 2
CALL set_counter(@counter,1); -- 3
CALL set_counter(@counter,5); -- 8
SELECT @counter; -- 8
In this tutorial, we have shown you how to define parameters in stored procedures, and introduced you to different parameter modes: IN, OUT, and INOUT.