title: How to use clause Except in queryable context
body: <p>I'm using Asp.Net Core com Scaffolding generate context and models.<br>
  I need to check an except comparison between 2 tables. </p>
  
  <p>In SQL server this work:</p>
  
  <pre><code>SELECT Id FROM AspNetUsers a
  EXCEPT 
  SELECT UserId FROM OtherClass
  </code></pre>
  
  <p>But in context not working. I tried this:</p>
  
  <p>How can I implement these parameters?: <code>_context.AspNetUsers.Except()</code><br>
  I tried with <code>.FromSql</code> unsuccessfully</p>
  
  <pre><code>public IActionResult Create()
  {
      ViewData["UserId"] = new SelectList(_context.AspNetUsers.FromSql(@"SELECT Id FROM AspNetUsers a EXCEPT SELECT UserId FROM OtherClass"), "Id", "UserName");
      return View();
  }
  </code></pre>