title: Indexing four columns?
body: <p>I have a table that I use to retrieve drive times, according to longitude and latitude of the origin and destination.  Although I am using Google's API to find new commute times, I store the results of previous queries locally so that if I need to query the same drive again, I won't have to use Google.  (Google's web service is throttled.)  Anyway, the table includes five columns:</p>
  
  <pre><code>    LatStart (smallmoney)
      LongStart (smallmoney)
      LatEnd (smallmoney)
      LongEnd (smallmoney)
      DriveTime (Int.  In seconds)
  </code></pre>
  
  <p>(Smallmoney, it turns out, works very well for longitude and latitude, as long as you only need four digits after the decimal, which is precise enough for this.)</p>
  
  <p>My question is: <strong><em>For optimal performance in SELECT queries, should I index all four longitude / Latitude columns?</em></strong></p>
  
  <p>And a second question: We can assume that it won't delete very often, but in the long run as the table grows, it will still insert rows about 25% as often as it selects rows.  <strong><em>Therefore, will an index on all four columns be detrimental to insert queries?</em></strong></p>