title: Create Unqiue case-insensitive constraint on two varchar fields
body: <p>In Oracle 10g, how do I add a unique case-insensitive constraint on two varchar fields?  For example, given the following records already in the table:</p>
  
  <pre><code>"Stephen", "Swensen"
  "John", "Smith"
  </code></pre>
  
  <p>The following inserts would be invalid:</p>
  
  <pre><code>"stephen", "Swensen"
  "John", "smith"
  "stephen", "swensen"
  </code></pre>
  
  <p>But the following inserts would be valid:</p>
  
  <pre><code>"Stephen", "Smith"
  "John", "Swensen"
  </code></pre>