How can you use a cursor in SQL DB2 stored procedures?

1 Declare a cursor

The first step to use a cursor in SQL DB2 stored procedures is to declare it. A cursor declaration consists of a name, a keyword CURSOR, and a SELECT statement that defines the query result set. You can also specify some options, such as WITH HOLD, FOR READ ONLY, or FOR UPDATE, to control the cursor behavior and the concurrency level. Here is an example of a cursor declaration:

DECLARE customer_cursor CURSOR WITH HOLD FOR
SELECT name, email, phone FROM customers;        

2 Open a cursor

After declaring a cursor, you need to open it before you can fetch any data from it. Opening a cursor executes the SELECT statement and creates a result set that the cursor can access. You can use the OPEN statement to open a cursor, optionally with a USING clause to pass parameters to the SELECT statement. Here is an example of opening a cursor: OPEN customer_cursor USING country_code;

3 Fetch a cursor

Once a cursor is open, you can fetch data from it using the FETCH statement. The FETCH statement retrieves the next row from the result set and assigns the values to the specified variables. You can also use a loop structure, such as WHILE, REPEAT, or FOR, to fetch multiple rows until the cursor reaches the end of the result set. Here is an example of fetching a cursor:

FETCH customer_cursor INTO customer_name, customer_email, customer_phone;
WHILE SQLCODE = 0 DO
 -- do something with the fetched data
 FETCH customer_cursor INTO customer_name, customer_email, customer_phone;
END WHILE;        

4 Close a cursor

When you are done with fetching data from a cursor, you should close it to release the resources associated with it. Closing a cursor terminates the result set and frees the memory used by the cursor. You can use the CLOSE statement to close a cursor, as shown in this example: CLOSE customer_cursor;

5 Deallocate a cursor

In some cases, you may also need to deallocate a cursor to remove its definition from the stored procedure. Deallocating a cursor allows you to reuse the same name for another cursor declaration. You can use the DEALLOCATE statement to deallocate a cursor, as shown in this example: DEALLOCATE customer_cursor; Using a cursor in SQL DB2 stored procedures can help you handle complex data manipulation tasks that require row-by-row processing. However, you should also be aware of the performance and concurrency implications of using cursors, and use them only when necessary.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?