title: Getting warning: Null value is eliminated by an aggregate or other SET operation
body: <p>I have this schema</p>
  
  <pre><code>create table t(id int, d date) 
  
  insert into t (id, d) values (1, getdate()), 
                               (2, NULL)
  </code></pre>
  
  <p>When doing</p>
  
  <pre><code>declare @mindate date    
  select @mindate = min(d) from t
  </code></pre>
  
  <p>I get the warning</p>
  
  <blockquote>
    <p>Null value is eliminated by an aggregate or other SET operation</p>
  </blockquote>
  
  <p>Why and what can I do about it?</p>