title: With multiple sql order by clause, is all order bys run even if earlier order by has proved that the rows are not equal?
body: <p>In a SQL query with multiple <code>order by</code> clauses, is all of them really run during execution?</p>
  
  <p>Example:</p>
  
  <pre><code>select * from my_table
  order by field5, field3, field2
  </code></pre>
  
  <p>If the the list after execution of 'order by' field5 and field3 has a unique list whit only one combination of field5 and field3, is 'order by field2' still run during execution of SQL query? Or is, in my case SQL Server, smart enough to see this and skip the last step?</p>
  
  <p>I'm asking because I am writing a stored procedure where I have a list where I'm most of the time only would need to order by to or three columns, but in some cases I would like to order by a last column if necessary, but this will be an alpha numeric sorting and this will slow down the query, so of course I would like to avoid it as much as possible... </p>