title: How do composite indexes work?
body: <p>I've created composite indexes (<em>indices</em> for you mathematical folk) on tables before with an assumption of how they worked. I was just curious if my assumption is correct or not.</p>
  
  <p>I assume that when you list the order of columns for the index, you are also specifying how the indexes will be grouped. For instance, if you have columns <code>a</code>, <code>b</code>, and <code>c</code>, and you specify the index in that same order <code>a ASC</code>, <code>b ASC</code>, and <code>c ASC</code> then the resultant index will essentially be many indexes for each "group" in <code>a</code>.</p>
  
  <p>Is this correct? If not, what will the resultant index actually look like?</p>