How to work with non-scrollable cursors in SQL for specific use cases

19 Sep 2023

When working with large datasets in SQL, you may often come across situations where you need to process data in a forward-only manner, without the ability to scroll back or move to arbitrary rows. SQL provides non-scrollable cursors that are specifically designed for these use cases. In this article, we will explore how to work with non-scrollable cursors and discuss some specific use cases where they can be beneficial.

What are Non-Scrollable Cursors?

A cursor in SQL acts as a pointer to a result set retrieved from a query. By default, cursors are scrollable, meaning you can move backward, forward, or jump to a specific row within the result set. However, non-scrollable cursors restrict this movement to a forward-only direction, allowing you to iterate through the result set only once from start to end.

Use Cases for Non-Scrollable Cursors

1. Bulk Data Processing

When dealing with large datasets, it is often more efficient to process the data in bulk rather than fetching and processing individual records. Non-scrollable cursors are ideal for such scenarios. You can use a non-scrollable cursor to retrieve a batch of records from the result set, process them, and then fetch the next batch until you reach the end.

Example code:

DECLARE @ID INT
DECLARE myCursor CURSOR FAST_FORWARD FOR
SELECT ID FROM YourTable

OPEN myCursor
FETCH NEXT FROM myCursor INTO @ID

WHILE @@FETCH_STATUS = 0
BEGIN
    -- Perform bulk processing on @ID

    FETCH NEXT FROM myCursor INTO @ID
END

CLOSE myCursor
DEALLOCATE myCursor

2. Streaming Data

In some cases, you may need to process a continuous stream of data in real-time. Non-scrollable cursors provide an efficient way to handle such scenarios, as they allow you to fetch and process records one by one as they become available. This can be particularly useful for applications that require near real-time processing, such as streaming analytics or event-based systems.

Example code:

DECLARE @Name NVARCHAR(50)
DECLARE myCursor CURSOR FORWARD_ONLY FOR
SELECT Name FROM YourTable ORDER BY DateColumn ASC

OPEN myCursor
FETCH NEXT FROM myCursor INTO @Name

WHILE @@FETCH_STATUS = 0
BEGIN
    -- Process record with @Name

    FETCH NEXT FROM myCursor INTO @Name
END

CLOSE myCursor
DEALLOCATE myCursor

Conclusion

Non-scrollable cursors provide a valuable tool for specific use cases where forward-only processing is required. Whether you are dealing with bulk data processing or streaming data, non-scrollable cursors can help you efficiently process large datasets in a forward-only manner. By leveraging this SQL feature effectively, you can improve the performance and scalability of your data processing workflows.

#SQL #NonScrollableCursors #DataProcessing