SQL Antipatterns, Volume 1

How can I tell what I think till I see what I say?

E. M. Forster

Chapter 19Implicit Columns

A PHP programmer asked for help troubleshooting the confusing result of a seemingly straightforward SQL query against his library database:

Implicit-Columns/intro/join-wildcard.sql

SELECT * FROM Books b JOIN Authors a ON (b.author_id = a.author_id);

This query returned all book titles as null. Even stranger, when he ran a different query without joining to the Authors, the result included the real book titles as expected.

The cause of his trouble was that the PHP database extension he was using returned each row resulting from the SQL query as an associative array. For example, he could access the Books.isbn column as $row["isbn"]. In ...