title: SQL update only when non null
body: <pre><code>UPDATE main
  SET main.PCH_2YR =
  (SELECT TOP 1 sub.PCH_2YR FROM [dbGlobalPricingMatrix].[dbo].[tblPCHLookup_Test] sub WHERE
  sub.capid = main.capid AND
  sub.milespa = main.mileage AND
  sub.maintained = main.maintenance AND sub.pch_2yr IS NOT NULL)
  FROM [dbWebsiteLO3-PRICING]..Vehicles_Staging_Data main
  </code></pre>
  
  <p>I only want to set the value if the subquery returns a value that isn't <code>NULL</code>. How can I do that?</p>
  
  <p>Only one row will ever match the conditions, but I only want to use it's value if it's not NULL. </p>