title: Computed bit column that returns whether another column is null
body: <p>I try to have this computed column:</p>
  
  <pre><code>CREATE TABLE dbo.Item
  (
      ItemId int NOT NULL IDENTITY (1, 1),
      SpecialItemId int NULL,
      --I tried this
      IsSpecialItem AS ISNULL(SpecialItemId, 0) &gt; 0, 
      --I tried this
      IsSpecialItem AS SpecialItemId IS NOT NULL
      --Both don't work
  )  ON [PRIMARY]
  </code></pre>