MySQL Stored Procedures: Output Parameters Explained

What Are Output Parameters?

Output parameters are special variables declared in a stored procedure that allow the procedure to return values to the caller.

Unlike input parameters, which provide data to the procedure, output parameters send data back after execution.

• Declared using the OUT keyword in the procedure signature.
• Can return any valid MySQL data type.
• Allow multiple values to be returned from a single procedure call.

Defining Output Parameters in MySQL

To define an output parameter, use the OUT keyword before the parameter name and specify its data type.

You can mix IN, OUT, and INOUT parameters in the same procedure.

• Syntax example: CREATE PROCEDURE proc_name (IN param1 INT, OUT param2 VARCHAR(50))
• Inside the procedure, assign values to the output parameter using SET or SELECT.

Calling Stored Procedures with Output Parameters

When calling a procedure with output parameters, you must declare variables to receive the output values.

Use the CALL statement and pass variables for output parameters to capture the returned data.

• Declare variables using the DECLARE statement in stored programs or SET in client sessions.
• Example: CALL proc_name(input_value, @output_var);
• Retrieve the output value using SELECT @output_var;

Practical Example: Using Output Parameters

Let's create and call a stored procedure that calculates the total sales for a given customer and returns it via an output parameter.