title: Finding rows that have many similar values and one different one
body: <p>I'm trying to isolate a problem with a violation of a unique key index. I'm pretty certain that the cause is resulting from columns that have the same value in 3 columns not having the same value in the 4th (when they should). As an example...</p>
  
  <pre><code>Key   Column1   Column2   Column3   Column4
  1       A          B         C         D
  2       A          B         C         D
  3       A          B         C         D
  4       A          B         C         Z
  </code></pre>
  
  <p>I basically want to select column 4, or some way to let me identify column 4. I know it's a matter of using aggregrate functions but I'm not very familiar with them. Can anyone assist on a way to select Key, Column4 for rows that have a different column 4 value and the same column 1-3 values?</p>