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copied!<p>When you <code>INSERT</code> new records, given that you don't want to do two inserts for some reason, <a href="http://dev.mysql.com/doc/refman/5.0/en/triggers.html" rel="nofollow">using a trigger</a> to insert into the second table will work. For <code>UPDATE</code> and <code>DELETE</code> you might want to look at the <code>CASCADE</code> option with <a href="http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html" rel="nofollow">foreign keys</a>. If all you are doing is keeping the data consistent between tables, that's exactly what cascade is for.</p> <p>When you create table2 you just add a foreign key like this:</p> <pre><code>FOREIGN KEY (id, username) REFERENCES table1(id, username) ON UPDATE CASCADE ON DELETE CASCADE </code></pre> <p>Then whenever you alter table1 the changes will automatically get pushed through to table2. </p> <p><strong>Couple prerequisites for this to work:</strong></p> <ol> <li>You have to use a <a href="http://dev.mysql.com/doc/refman/5.1/en/storage-engines.html" rel="nofollow">storage engine</a> that supports foreign keys, something like <code>InnoDB</code> and not <code>MyISAM</code></li> <li>You need to have an index on <code>(id,username)</code> in table1; the foriegn key needs to match a key in the parent table</li> <li>You should read the doc page for <a href="http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html" rel="nofollow">foreign keys</a>. There are a couple other ways you can tweak them, and you should figure out what works best for your purposes.</li> </ol>

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