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copied!<p>You can use a lookup table with a VARCHAR primary key, and your main data table uses a FOREIGN KEY on its column, with cascading updates.</p> <pre><code>CREATE TABLE ColorLookup ( color VARCHAR(20) PRIMARY KEY ); CREATE TABLE ItemsWithColors ( ...other columns..., color VARCHAR(20), FOREIGN KEY (color) REFERENCES ColorLookup(color) ON UPDATE CASCADE ON DELETE SET NULL ); </code></pre> <p>This solution has the following advantages:</p> <ul> <li>You can query the color names in the main data table without requiring a join to the lookup table.</li> <li>Nevertheless, color names are constrained to the set of colors in the lookup table.</li> <li>You can get a list of unique colors names (even if none are currently in use in the main data) by querying the lookup table.</li> <li>If you change a color in the lookup table, the change automatically cascades to all referencing rows in the main data table.</li> </ul> <hr> <p>It's surprising to me that so many other people on this thread seem to have mistaken ideas of what "normalization" is. Using a surrogate keys (the ubiquitous "id") has nothing to do with normalization!</p> <hr> <p>Re comment from @MacGruber:</p> <p>Yes, the size is a factor. In InnoDB for example, every secondary index stores the primary key value of the row(s) where a given index value occurs. So the more secondary indexes you have, the greater the overhead for using a "bulky" data type for the primary key. </p> <p>Also this affects foreign keys; the foreign key column must be the same data type as the primary key it references. You might have a small lookup table so you think the primary key size in a 50-row table doesn't matter. But that lookup table might be referenced by millions or <em>billions</em> of rows in other tables!</p> <p>There's no right answer for all cases. Any answer can be correct for different cases. You just learn about the tradeoffs, and try to make an informed decision on a case by case basis.</p>

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