title: Excluding records where criteria meets
body: <p>I have a set of records where we identify several items connected to a customer. 
  My dilemma is that if a customer has both items then I would like to exclude that customer.</p>
  
  <p>If they only have one specific item then I want to include it.
  I will be using this code to create a view so i'm trying to find the best way. I could try <code>Row_number()</code> to identify different records, but I'm not sure that would be ideal in this situation.</p>
  
  <p>Example data table:</p>
  
  <pre><code>Customer | ItemID | value1 | Value2
     A         12       35       0
     B         12       35       0
     C         13       0        25
     C         12       0        25
     D         18       225       12
  </code></pre>
  
  <p>Desired Output:</p>
  
  <pre><code> Customer | ItemID | value1 | Value2
     A         12       35       0
     B         12       35       0
  </code></pre>
  
  <p>This is what I have so far:</p>
  
  <pre><code>select Customer, ItemID, Value1, Value2
  from Table1 
  where itemID = 12
  </code></pre>
  
  <p>This would give me customer <code>'C'</code>, which I don't want.</p>