Stored Procedures and Functions in DB2

Introduction

DB2, developed by IBM, provides support for stored procedures and functions. These database objects encapsulate a set of SQL statements and can be called and executed from within other SQL statements or applications. Stored procedures and functions offer advantages such as code reuse, enhanced security, and improved performance. In this tutorial, we will explore how to work with stored procedures and functions in DB2, including creating, executing, and managing them.

Creating a Stored Procedure in DB2

To create a stored procedure in DB2, you can use the CREATE PROCEDURE statement. Here's an example:

CREATE PROCEDURE GetEmployeeDetails (IN empID INT)


LANGUAGE SQL
BEGIN
SELECT EmployeeName, Department, Salary
FROM Employees
WHERE EmployeeID = empID;
END;

This command creates a stored procedure named "GetEmployeeDetails" that takes an input parameter "empID" and retrieves the employee name, department, and salary from the "Employees" table based on the specified employee ID.

Stored procedures can be written in different languages, such as SQL, SQL PL, or external languages like Java or C.

Executing a Stored Procedure in DB2

To execute a stored procedure in DB2, you can use the CALL statement. Here's an example:

CALL GetEmployeeDetails(1001);

This command calls the "GetEmployeeDetails" stored procedure with the employee ID parameter set to 1001. The stored procedure will execute and return the employee details for the specified ID.

You can also execute stored procedures from within other SQL statements, such as SELECT, INSERT, or UPDATE, to perform complex operations.

Creating a Function in DB2

To create a function in DB2, you can use the CREATE FUNCTION statement. Here's an example:

CREATE FUNCTION CalculateSalary (IN empID INT)


RETURNS DECIMAL(10,2)
LANGUAGE SQL
BEGIN
DECLARE salary DECIMAL(10,2);
SELECT Salary INTO salary
FROM Employees
WHERE EmployeeID = empID;
RETURN salary * 1.1;
END;

This command creates a function named "CalculateSalary" that takes an input parameter "empID" and returns the calculated salary for the specified employee ID. The function retrieves the employee's salary from the "Employees" table, multiplies it by 1.1 (to account for a 10% increase), and returns the result.

Functions in DB2 can have input parameters and return values of different data types.

Common Mistakes to Avoid

• Not properly validating user input within stored procedures and functions, leading to potential security vulnerabilities.
• Overcomplicating stored procedures or functions by including too many SQL statements or complex logic.
• Not considering the performance impact of executing resource-intensive operations within stored procedures or functions.
• Forgetting to handle errors and exceptions within the stored procedure or function code.
• Not documenting stored procedures and functions properly, making it difficult for others to understand and maintain the code.

Frequently Asked Questions (FAQs)

1. Q: What is the difference between a stored procedure and a function?

   A: A stored procedure is used to perform an action, such as inserting or updating data, and can have output parameters. A function, on the other hand, is used to calculate and return a value, and can be used within SQL statements.

2. Q: Can I call a stored procedure or function from an application?

   A: Yes, stored procedures and functions can be called from applications using SQL statements or application programming interfaces (APIs).

3. Q: Can stored procedures and functions have multiple input parameters?

   A: Yes, stored procedures and functions can have multiple input parameters, allowing for more flexibility in processing and calculations.

4. Q: Can I modify a stored procedure or function after it has been created?

   A: Yes, you can use the ALTER PROCEDURE or ALTER FUNCTION statement to modify the definition of a stored procedure or function, respectively.

5. Q: Can I drop a stored procedure or function from the database?

   A: Yes, you can use the DROP PROCEDURE or DROP FUNCTION statement to remove a stored procedure or function from the database.

Summary

In this tutorial, we explored stored procedures and functions in DB2. We learned how to create stored procedures to encapsulate SQL statements and how to execute them using the CALL statement. We also saw how to create functions to calculate and return values and how to use them within SQL statements. Additionally, we discussed common mistakes to avoid when working with stored procedures and functions and provided answers to some frequently asked questions related to this topic. With this knowledge, you can leverage stored procedures and functions to enhance code reusability, improve performance, and ensure data integrity in your DB2 databases.