How to Optimally Generate an Auxiliary Number Table in SQL?

Optimizing SQL Auxiliary Number Table Generation

Many SQL applications benefit from an auxiliary table containing a sequential range of numbers. This table can be pre-populated with a fixed number of rows, or generated dynamically using a function.

Traditional Approaches and Their Drawbacks

Common methods for creating such tables include recursive CTEs, while loops, cross joins, and more complex techniques like Itzik's method. However, these methods suffer from performance issues, particularly when generating large number sequences. Recursive CTEs, in particular, exhibit significant performance degradation with increasing row counts. While loops also show suboptimal performance.

Performance Benchmarking and Optimal Solution

Performance testing reveals the limitations of traditional approaches. A user-defined function consistently outperforms other methods, avoiding repeated computations for each query.

The High-Performance Function

The most efficient solution involves a user-defined function (UDF). This T-SQL function provides a highly optimized method:

<code class="language-sql">CREATE FUNCTION dbo.GetNumberSequence (@Start INT, @End INT)
RETURNS TABLE AS
RETURN
WITH NumberList AS (
    SELECT @Start AS Number
    UNION ALL
    SELECT Number + 1
    FROM NumberList
    WHERE Number < @End
)
SELECT Number
FROM NumberList;</code>

This function takes a start and end integer as input and returns a table containing the specified number sequence.

Summary

Using this user-defined function offers a significant performance advantage over other methods for generating auxiliary number tables in SQL. This approach minimizes overhead and ensures optimal query execution, regardless of the size of the required number sequence.

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