MySql `id` column has a 'PRIMARY' and a 'UNIQUE' index, is this ideal?
<p>Everything I can find on the internet explains the <em>difference</em> between these types of indexing, that is NOT my question.</p>

<p>When I create a new table in a database, I always create an id primary key as I'm sure most people do. I always make it <code>PRIMARY KEY, NOT NULL, UNIQUE, AUTO_INCREMENT</code>.</p>

<p>I'm recently getting big into adding custom indexes and I've noticed that my id field has these two index's (automatically created, for obvious reasons): </p>

<pre><code>There is a PRIMARY index
There is also a UNIQUE index
</code></pre>

<p>My assumption is due to the PK flag (primary key) the 'PRIMARY' index was automatically generated, and due to the <code>UNIQUE</code> flag  the 'UNIQUE' index was created.</p>

<p>I assume having two indexes on the same column is adding unnecessary overhead. My question is, is this true? Should I remove one of these index's? Or is it normal/ideal to have both of these index's created on my id column?</p>