mathematical formula

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As SQL developers, we tend to think of performance tuning in terms of crafting the best table indices, avoiding scalar and table valued functions, and analyzing query plans (among other things). But sometimes going back to the spec and applying some properties of elementary math can be the best way to begin to improve performance of SQL queries which implement mathematical formulas. This article is a case study of how I used this technique to optimize my SQL implementation of the Inverse Simpson Index.

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2021-05-07 (first published: 2019-09-12)

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There is a table tmp_tab:

CREATE TABLE tmp_tab (
id int,
val int
);

INSERT INTO tmp_tab VALUES
(1, 1),
(2, NULL),
(3, 3),
(4, 4),
(5, 5);

You want to order the rows ids by the following expression:

    ISNULL(val, id) + 1

Which of the following queries produces the expected ordering and why? (Select all correct)

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mathematical formula

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