Stored Procedures in Db2

In this article, we will provide a comprehensive guide on stored procedures in IBM Db2 Database.

What is a Stored Procedure?

A stored procedure is a pre-compiled database object that contains SQL code and other programming constructs like conditional statements, loops, etc. The stored procedure can be invoked by passing parameters to it, which are then used by the SQL code within the stored procedure to perform data manipulation or retrieval operations. Stored procedures are stored on the database server and can be executed multiple times without having to re-compile them every time they are called.

Benefits of Using Stored Procedures in IBM Db2 Database

1. Improved Performance:

Stored procedures improve performance by reducing the amount of parsing, planning, and optimization that occurs each time an SQL statement is executed. Since stored procedures are pre-compiled, they are executed faster than regular SQL statements, which require re-compiling each time they are executed.

2. Reusability:

Stored procedures are reusable code modules that can be invoked multiple times within the same application or different applications as well. This means developers do not have to write the same code repeatedly, reducing development time and effort.

3. Security:

Stored procedures provide an additional layer of security by allowing developers to limit access to the SQL code within the stored procedure. This is achieved by granting permissions to specific users or groups who are authorized to invoke the stored procedure.

4. Scalability:

Stored procedures can be used to perform complex data manipulation and retrieval operations, which can help in scaling applications as they grow in size and complexity.

Creating a Stored Procedure in IBM Db2 Database

To create a stored procedure in IBM Db2 Database, follow the steps below:

1. Connect to the database server using SQL commands or a GUI tool like SQL Monitor.

2. Use the CREATE PROCEDURE statement to define the stored procedure. The syntax for creating a stored procedure is as follows:

CREATE PROCEDURE <procedure_name>(<parameter_list>)
BEGIN ATOMIC
    [DECLARE VARIABLES SECTION]
    [SET VARIABLES SECTION]
    [EXECUTE SQL STATEMENTS SECTION]
END;

Where,

• <procedure_name> is the name of the stored procedure.
• <parameter_list> is a comma-separated list of parameters that can be passed to the stored procedure.
• [DECLARE VARIABLES SECTION] is an optional section where variables can be declared and initialized.
• [SET VARIABLES SECTION] is another optional section where variables can be set or updated.
• [EXECUTE SQL STATEMENTS SECTION] contains the actual SQL code that performs data manipulation or retrieval operations.

3. After defining the stored procedure, use the GRANT statement to grant permission to specific users or groups who are authorized to invoke the stored procedure. The syntax for granting permission is as follows:

GRANT EXECUTE ON <procedure_name>(<parameter_list>) TO <username>;

Where,

• <username> is the name of the user or group who is authorized to invoke the stored procedure.

4. Finally, use the CALL statement to execute the stored procedure. The syntax for calling a stored procedure is as follows:

CALL <procedure_name>(<parameter_list>)

Where,

• <procedure_name> is the name of the stored procedure.
• <parameter_list> is a comma-separated list of parameters that need to be passed to the stored procedure.

Examples of Using Stored Procedures in IBM Db2 Database

1. Creating a Stored Procedure to Insert Data into a Table:

Suppose we have a table named "customers" with columns "customer_id", "first_name", and "last_name". We want to create a stored procedure that inserts data into this table when called. The following code demonstrates how to create such a stored procedure:

CREATE PROCEDURE insert_customer(IN first_name VARCHAR(50), IN last_name VARCHAR(50))
BEGIN ATOMIC
    INSERT INTO customers (first_name, last_name) VALUES (first_name, last_name);
END;

This stored procedure takes two parameters, "first_name" and "last_name", which are used to insert data into the "customers" table. To execute this stored procedure, we can use the following code:

CALL insert_customer('John', 'Doe');

This will insert a new row with values "John" and "Doe" in columns "first_name" and "last_name", respectively.

2. Creating a Stored Procedure to Retrieve Data from a Table:

Suppose we have a table named "orders" with columns "order_id", "customer_id", and "total_amount". We want to create a stored procedure that retrieves data from this table when called. The following code demonstrates how to create such a stored procedure:

CREATE PROCEDURE retrieve_order(IN customer_id INTEGER)
BEGIN ATOMIC
    SELECT * FROM orders WHERE customer_id = customer_id;
END;

This stored procedure takes one parameter, "customer_id", which is used to retrieve data from the "orders" table. To execute this stored procedure, we can use the following code:

CALL retrieve_order(1234);

This will retrieve all rows from the "orders" table where "customer_id" equals 1234.

Conclusion

In conclusion, stored procedures are a powerful feature in IBM Db2 Database that can help developers to improve performance, reduce development time and effort, increase security, and scale applications as they grow in size and complexity. By following the steps outlined in this article, developers can create their own stored procedures for data manipulation or retrieval operations and execute them using SQL commands or GUI tools like SQL Monitor.