How to implement cursor-based pagination with keyset-based scrolling in SQL Server

19 Sep 2023

In SQL Server, implementing pagination efficiently is essential to enhance user experience and optimize query performance. Cursor-based pagination with keyset-based scrolling is a popular technique that enables efficient retrieval of paginated data without the need to count the total number of results.

What is Cursor-Based Pagination with Keyset-Based Scrolling?

Cursor-based pagination with keyset-based scrolling is a technique that uses a combination of cursors and keysets to paginate through large result sets effectively. The approach revolves around using a unique identifier or keyset of the last fetched record to determine the starting point for the next page.

Step-by-Step Implementation in SQL Server

Let’s walk through the implementation of cursor-based pagination with keyset-based scrolling in SQL Server:

Order the Result Set: To implement keyset-based scrolling, it’s crucial to have your result set ordered by a unique column or set of columns. For example, if you have a table of users, you can order the result set by the unique user ID.

Declare and Open a Cursor: Declare a cursor using the DECLARE CURSOR statement and associate it with the ordered result set using the SELECT statement. For instance:

DECLARE @cursor CURSOR
DECLARE @keyset NVARCHAR(MAX)

SET @cursor = CURSOR FORWARD_ONLY STATIC FOR
SELECT keysetColumn, otherColumns
FROM yourTable
ORDER BY keysetColumn ASC
OPEN @cursor

Fetch Data for a Page: Use the FETCH statement to retrieve a specified number of rows for a given page. The keyset column value from the last fetched row serves as the reference for the starting point of the next page. Here’s an example:
```
FETCH NEXT FROM @cursor INTO @keyset, otherColumns
```
Use the Fetched Data: Process and display the fetched data for the current page. You could return the result set to an application or use it for further processing.
Repeat for Next Pages: To fetch the next page of data, repeat the FETCH NEXT statement using the previous keyset value as the starting point. Keep fetching until you reach the desired number of rows or until there are no more rows to fetch.
Close and Deallocate the Cursor: After all the required data has been fetched, close and deallocate the cursor using the CLOSE and DEALLOCATE statements, respectively.

Benefits of Cursor-Based Pagination with Keyset-Based Scrolling

Cursor-based pagination with keyset-based scrolling provides several benefits compared to traditional offset-based pagination:

Improved Query Performance: This technique avoids the need to generate and scan a large number of rows for each page, resulting in improved query performance as the data size grows.
Consistent Results: Unlike offset-based pagination, keyset-based scrolling ensures consistent results, even if new rows are inserted or existing rows are updated or deleted during pagination.
Scalability and Flexibility: Keyset-based scrolling scales better with large result sets and allows users to jump to specific pages without the performance degradation associated with offset-based pagination.

#pagination #SQLServer