MySQL Stored Procedure Parameters

Summary: in this tutorial, you will learn how to create stored procedures with parameters, including IN, OUT, and INTOUT parameters.

Introduction to MySQL stored procedure parameters

Typically, stored procedures have parameters, making them more useful and reusable.

A parameter in a stored procedure has one of three modes: IN, OUT, or INOUT.

IN parameters

IN is the default mode. When defining an IN parameter in a stored procedure, the calling program must pass an argument to the stored procedure.

Additionally, the value of an IN parameter is protected. This means that even if you change the value of the IN parameter inside the stored procedure, its original value remains unchanged after the stored procedure ends. In other words, the stored procedure works only on the copy of the IN parameter.

OUT parameters

The value of an OUT parameter can be modified within the stored procedure, and its updated value is then passed back to the calling program.

Note that stored procedures cannot access the initial value of the OUT parameter when they begin.

INOUT parameters

An INOUT  parameter is a combination of IN and OUT parameters. This means that the calling program may pass the argument, and the stored procedure can modify the INOUT parameter and pass the new value back to the calling program.

Defining a parameter

Here is the basic syntax for defining a parameter in stored procedures:

[IN | OUT | INOUT] parameter_name datatype[(length)]Code language: SQL (Structured Query Language) (sql)

In this syntax,

• First, specify the parameter mode, which can be IN , OUT or INOUT depending on the purpose of the parameter in the stored procedure.
• Second, provide the name of the parameter. The parameter name must follow the naming rules of the column name in MySQL.
• Third, define the data type and maximum length of the parameter.

MySQL stored procedure parameter examples

Let’s explore some examples of using stored procedure parameters.

The IN parameter example

The following example creates a stored procedure that finds all offices that are located in a country specified by the input parameter countryName:

DELIMITER //

CREATE PROCEDURE GetOfficeByCountry(
	IN countryName VARCHAR(255)
)
BEGIN
	SELECT * 
 	FROM offices
	WHERE country = countryName;
END //

DELIMITER ;Code language: SQL (Structured Query Language) (sql)

In this example, the countryName is the IN parameter of the stored procedure.

Suppose that you want to find offices located in the USA, you need to pass an argument (USA) to the stored procedure as shown in the following query:

CALL GetOfficeByCountry('USA');Code language: SQL (Structured Query Language) (sql)

To find offices in France, you pass the literal string France to the GetOfficeByCountry stored procedure as follows:

CALL GetOfficeByCountry('France')Code language: SQL (Structured Query Language) (sql)

Because the countryName is the IN parameter, you must pass an argument. If you don’t do so, you’ll get an error:

CALL GetOfficeByCountry();Code language: SQL (Structured Query Language) (sql)

Here’s the error:

Error Code: 1318. Incorrect number of arguments for PROCEDURE classicmodels.GetOfficeByCountry; expected 1, got 0Code language: JavaScript (javascript)

The OUT parameter example

The following defines a stored procedure that returns the number of orders based on their order status.

DELIMITER $$

CREATE PROCEDURE GetOrderCountByStatus (
	IN  orderStatus VARCHAR(25),
	OUT total INT
)
BEGIN
	SELECT COUNT(orderNumber)
	INTO total
	FROM orders
	WHERE status = orderStatus;
END$$

DELIMITER ;Code language: SQL (Structured Query Language) (sql)

The stored procedure GetOrderCountByStatus() has two parameters:

• The orderStatus is the IN parameter specifies the status of orders to return.
• The total is the OUT parameter that stores the number of orders in a specific status.

To find the number of orders that already shipped, you call GetOrderCountByStatus and pass the order status as of Shipped, and also pass a session variable ( @total ) to receive the return value.

CALL GetOrderCountByStatus('Shipped',@total);
SELECT @total;Code language: SQL (Structured Query Language) (sql)

Output:

+--------+
| @total |
+--------+
|    303 |
+--------+
1 row in set (0.00 sec)Code language: JavaScript (javascript)

To get the number of orders that are in process, you call the stored procedure GetOrderCountByStatus as follows:

CALL GetOrderCountByStatus('In Process',@total);
SELECT @total AS total_in_process;Code language: SQL (Structured Query Language) (sql)

Output:

+------------------+
| total_in_process |
+------------------+
|                6 |
+------------------+
1 row in set (0.00 sec)Code language: JavaScript (javascript)

The INOUT parameter example

The following example demonstrates how to use an INOUT parameter in a stored procedure:

DELIMITER $$

CREATE PROCEDURE SetCounter(
	INOUT counter INT,
    IN inc INT
)
BEGIN
	SET counter = counter + inc;
END$$

DELIMITER ;Code language: SQL (Structured Query Language) (sql)

In this example, the stored procedure SetCounter() accepts one INOUT parameter ( counter ) and one IN parameter ( inc ). It increases the counter ( counter ) by the value specified by the inc parameter.

These statements illustrate how to call the SetSounter stored procedure:

SET @counter = 1;
CALL SetCounter(@counter,1); -- 2
CALL SetCounter(@counter,1); -- 3
CALL SetCounter(@counter,5); -- 8
SELECT @counter; -- 8Code language: SQL (Structured Query Language) (sql)

Here is the output:

In this tutorial, you have learned how to create stored procedures with parameters including IN, OUT, and INOUT parameters.