title: How does indexing improve performance when joining two tables
body: <p>In one of our practice papers we are asked the question in the title.</p>
  
  <p>Most of the articles I've read say that indexing improves performance of joins, but does not tell me how.</p>
  
  <p>Maybe it's so obvious that it doesn't need to be stated. Indexing is essentially ordering a column right? So I guess having a column in order makes it easier to operate on. Is there more to it? Or am I overthinking it?</p>
  
  <p>Thanks</p>