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Sams Teach Yourself MySQL in 21 Days, Second Edition
book

Sams Teach Yourself MySQL in 21 Days, Second Edition

by Tony Butcher
December 2002
Beginner content levelBeginner
640 pages
16h 41m
English
Sams
Content preview from Sams Teach Yourself MySQL in 21 Days, Second Edition

Indexes

An index, also known as a key, provides a means of rapidly accessing specific rows of data within a table.

Indexes Explained

Suppose that you have a users table that holds details about many people. When you ask MySQL to retrieve all rows matching a given criterion, it reads through the entire table, row by row, retrieving data from all rows that match the criterion. Even if you want to retrieve only a single specific row, it must read every row of the table.

Reading through an entire table like this—an operation known as a table scan—does the job but is highly inefficient. That's where an index can help.

Say that we have a query in which we want to retrieve the row referenced by a given user_id in table users. The table might look like ...

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Publisher Resources

ISBN: 0672323923Purchase book