title: Slow SQL query when joining tables
body: <p>This query is very very slow and i'm not sure where I'm going wrong to cause it to be so slow. </p>
  
  <p>I'm guessing it's something to do with the flight_prices table<br>
  because if I remove that join it goes from 16 seconds to less than one.</p>
  
  <pre><code>    SELECT * FROM OPENQUERY(mybook,
      'SELECT  wb.booking_ref 
      FROM    web_bookings wb 
              LEFT JOIN prod_info pi ON wb.location = pi.location 
              LEFT JOIN flight_prices fp ON fp.dest_date = pi.dest_airport + '' '' + wb.sort_date
      WHERE   fp.dest_cheapest = ''Y'' 
              AND wb.inc_flights = ''Y'' 
              AND wb.customer = ''12345'' ')
  </code></pre>
  
  <p>Any ideas how I can speed up this join??</p>