title: Order of columns in an index
body: <p>I am working on a database with large number of rows (6 Mil+). </p>
  
  <p>This table has a composite primary key on two columns.</p>
  
  <p>It also has separate index on each of those fields as there are queries that require this. Obviously, one of those indexes (indices?) is redundant and slowing down performance for write operations. </p>
  
  <p>How do I find out which one is redundant? I understand the first column of a primary key is already indexed and need not be indexed separately. Is that correct? If so, is there a query I can run to find out which is the first one in the list?</p>