Hashtags: #SQL #Pagination

Pagination is a common requirement when working with large datasets. Cursor-based pagination, also known as keyset pagination, is a technique that allows you to retrieve a subset of data from a larger dataset efficiently. It provides a better user experience and reduces the load on your database.

In this blog post, we’ll learn how to implement cursor-based pagination with the OFFSET and FETCH clauses in SQL. This technique is widely supported across different database systems.

Step 1: Understanding the concept

Cursor-based pagination relies on using a unique identifier to keep track of the current position in the dataset. This unique identifier serves as the cursor, allowing us to fetch the next set of results.

Rather than using the OFFSET and LIMIT clauses, which can be inefficient for large datasets, we’ll use the FETCH clause to limit the number of rows returned per page. The cursor will be an attribute of the last row of each page, ensuring that we can pick up where we left off for the next page.

Step 2: Creating the initial query

To implement cursor-based pagination, we need a query to fetch the initial page of results. The query should be sorted in a predictable, consistent manner to ensure that subsequent pages are returned correctly.

SELECT *
FROM your_table
ORDER BY column_name
FETCH FIRST n ROWS ONLY;

Replace your_table with the name of your table and column_name with the column you want to sort by. n represents the number of rows to fetch per page.

Step 3: Fetching the next page

To fetch the subsequent pages, we need to modify the initial query by adding a WHERE clause that uses the cursor. The cursor should represent the last value of the column used for sorting in the previous page.

SELECT *
FROM your_table
WHERE column_name > last_cursor_value
ORDER BY column_name
FETCH FIRST n ROWS ONLY;

Replace last_cursor_value with the value of the column used for sorting in the last row of the previous page.

Step 4: Handling reverse pagination

If you want to implement reverse pagination, where newer results are returned first, you can modify the queries accordingly. In the initial query, use the DESC keyword in the ORDER BY clause. In the subsequent page query, change the WHERE clause to use the < operator instead of >.

Conclusion

Cursor-based pagination with the OFFSET and FETCH clauses provides an efficient method to paginate through large datasets in SQL. It avoids the performance issues associated with OFFSET and LIMIT, allowing you to retrieve pages of data quickly and seamlessly.

By implementing this pagination technique, you can enhance the user experience of your applications and optimize the performance of your database queries.

Remember to use the correct syntax for the database system you are using, as there might be slight variations in the syntax.