title: Does having several indices all starting with the same columns negatively affect Sybase optimizer speed or accuracy?
body: <p>We have a table with, say, 5 indices (one clustered).</p>
  
  <p>Question: will it somehow negatively affect optimizer performance - either speed or accuracy of index picks - if all 5 indices start with the same exact field? (all other things being equal). </p>
  
  <p>It was suggested by someone at the company that it may have detrimental effect on performance, and thus one of the indices needs to have the first two fields switched. </p>
  
  <p>I would prefer to avoid change if it is not necessary, since they didn't back up their assertion with any facts/reasoning, but the guy is senior and smart enough that I'm inclined to seriously consider what he suggests.</p>
  
  <p>NOTE1: The basic answer "tailor the index to the where clauses and overall queries" is not going to help me - the index that would be changed is a covered index for the only query using it and thus the order of the fields in it would not affect the IO amount. <a href="https://stackoverflow.com/questions/1463486/does-the-order-of-columns-on-a-covered-index-in-sybase-affect-select-performance">I have asked a separate SO question just to confirm that assertion.</a></p>
  
  <p>NOTE2: That field is a date when the records are inserted, and the table is pretty big, if this matters. It has data for ~100 days, about equal # of rows per date, and the first index is a clustered index starting with that date field.</p>