title: Why does this dropdown form filter work on a native table but not an ODBC linked table?
body: <p>I'm transitioning an Access user app from using native Access tables to using ODBC-linked SQL Server tables.</p>
  
  <p>I have a set of forms that are filtered by a selection from a dropdown (in a stand-alone selection form).  By design, if the user leaves the dropdown blank the form launches unfiltered.</p>
  
  <p>All of this works with the native tables, but when I try it using the linked tables I get an <code>ODBC--call failed</code> error</p>
  
  <p>The SQL query Access generated for the query I'm using as the Record Source of the form that is filtered is:</p>
  
  <pre><code>SELECT linked.ASSIGNED_CARE_COORDINATOR, [rest of the variables]
  WHERE (((linked.ASSIGNED_CARE_COORDINATOR)=[Forms]![frmCoord_Selector]![cmbCoords]))
  OR   (((([linked].[ASSIGNED_CARE_COORDINATOR]) 
       Like [Forms]![frmDeadline_Report_Coord_Selector]![cmbCoords]) Is Null));
  </code></pre>
  
  <p>I know the ODBC connection itself is fine; if I remove the code after <code>OR</code> the query works with the linked table, but of course doesn't have the show-all-if-null functionality.</p>
  
  <p>Why would this work with a native table but not the linked version of the exact same table?</p>