How Can Keyset Pagination Improve SQL Server Pagination Efficiency Over OFFSET?

SQL Server Pagination: Keyset Pagination vs. OFFSET

Using OFFSET for pagination in SQL Server can be inefficient with large datasets. Keyset pagination offers a superior alternative.

Understanding Keyset Pagination

Unlike rowset pagination (which scans all preceding rows), keyset pagination uses a unique index to directly access the starting point of a page. This significantly reduces unnecessary data retrieval. A unique index on the pagination key (and any additional query columns) is crucial for optimal performance.

Advantages of Keyset Pagination

• Enhanced Efficiency: Keyset pagination dramatically improves efficiency by avoiding the overhead of scanning irrelevant rows.
• Eliminates "Missing Row" Errors: Rowset pagination can lead to "missing row" issues if rows are deleted from previously retrieved pages. Keyset pagination avoids this since keys remain consistent.
• Page Number Limitation: Unlike rowset pagination, keyset pagination doesn't allow direct page number access. Instead, it navigates using the index key.

Implementation Example

Let's say we have a table named TableName with an index on Id, and we need to paginate using the latest Id value.

Initial Query (First Page):

<code class="language-sql">SELECT TOP (@numRows) *
FROM TableName
ORDER BY Id DESC;</code>

Subsequent Queries:

<code class="language-sql">SELECT TOP (@numRows) *
FROM TableName
WHERE Id < @lastId
ORDER BY Id DESC;</code>

Where @lastId is the lowest Id value from the previous page's results.

For columns lacking unique values, include a secondary column in both the `ORDER BY` and `WHERE` clauses, along with a composite index on both columns.

Important Considerations:

• The chosen key must be unique.
• Use `INCLUDE` to add extra columns to the index for improved performance.
• Handle `NULL` values appropriately.

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