In SQL, the ALTER PROCEDURE statement is used to modify an existing stored procedure. A stored procedure is a precompiled collection of one or more SQL statements that can be executed as a single unit. Modifying a stored procedure can be necessary to update its functionality, improve performance, or accommodate changes in the database schema.


Here’s the basic syntax for the ALTER PROCEDURE statement:

ALTER PROCEDURE procedure_name
[ { @parameter data_type } = value [ OUTPUT ] ]
[ ,...n ]
[ WITH  [ ,...n ] ]
    -- Updated procedure body

Let’s break down the components of this syntax:

procedure_name: Specifies the name of the stored procedure to be altered.

@parameter data_type: Defines parameters for the stored procedure, including their data types.

value: Assigns a default value to a parameter.

OUTPUT: Specifies that the parameter is an output parameter.

WITH : Defines additional options for the stored procedure.

AS: Begins the definition of the updated procedure body.


Here’s a simple example of how you might use the ALTER PROCEDURE statement:

-- Original stored procedure
    @EmployeeID INT
    SELECT * 
    FROM Employees 
    WHERE EmployeeID = @EmployeeID;

-- Altering the stored procedure to add a parameter
    @EmployeeID INT,
    @DepartmentID INT
    SELECT * 
    FROM Employees 
    WHERE EmployeeID = @EmployeeID 
    AND DepartmentID = @DepartmentID;

In this example, the original stored procedure GetEmployee is modified using ALTER PROCEDURE to include an additional parameter @DepartmentID. This alteration allows for more flexibility in querying employee information by both employee ID and department ID.

It’s important to note that the ALTER PROCEDURE statement is used to make changes to the body of the stored procedure and its parameters. If you need to modify other properties of the procedure, such as encryption options or permissions, you might need to use other statements or tools provided by the specific database management system you’re working with (e.g., Microsoft SQL Server, MySQL, PostgreSQL).