title: multi-column index order and IN queries
body: <p>In a multi-column index, I know that the order matters regarding which types of queries will be able to use the index. The columns mentioned in <code>WHERE</code> should be the leftmost columns in the index. <a href="http://www.postgresql.org/docs/9.3/static/indexes-multicolumn.html" rel="nofollow">Here's a Postgres article about that.</a></p>
  
  <p>But, consider the case where <strong>all</strong> columns are used. Does the order affect <strong>performance of using the index</strong> in these two scenarios:</p>
  
  <ol>
  <li>queries with multiple <code>=</code>. example: <code>SELECT * FROM "posts" WHERE "user_id" = 5 AND "post_type" = 'Thing' AND "state" = 'active'</code></li>
  <li>in queries involving an <code>IN</code>. example: <code>SELECT * FROM "posts" WHERE "user_id" = 5 AND "post_type" = 'Thing' AND ("state" IN ('active', 'draft'))</code></li>
  </ol>