SQL Antipatterns (for Amanda Dunlap) by Bill Karwin

Author:Bill Karwin
Language: eng
Format: epub
Tags: Pragmatic Bookshelf
ISBN: 1-934356-55-7
Publisher: The Pragmatic Bookshelf, LLC (212800)

SELECT * FROM Bugs WHERE assigned_to <> NULL;

The condition in a WHERE clause is satisfied only when the expression is true, but a comparison to NULL is never true; it’s unknown. It doesn’t matter whether the comparison is for equality or inequality; it’s still unknown, which is certainly not true. Neither of the previous queries return rows where assigned_to is null.

Using Null in Query Parameters

It’s also difficult to use null in a parameterized SQL expression as if the null were an ordinary value.

Fear-Unknown/anti/parameter.sql

SELECT * FROM Bugs WHERE assigned_to = ?;

The previous query returns predictable results when you send an ordinary integer value for the parameter, but you can’t use a literal NULL as the parameter.

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