title: SQL - delete rows where only one column changes
body: <p>I have a large table in SQL, in which an effective_from date column should update every time one of the other columns changes.  However, for some reason, there are numerous rows in which the effective_from date changes, but no other values have changed. For example:</p>
  
  <pre><code>CODE    NAME    EFFECTIVE_FROM
  CCWA    Oak     1999
  CCWA    Willow  2001
  CCWA    Willow  2004
  </code></pre>
  
  <p>How can I delete the rows where the change in effective_from date doesn't provide any info.  e.g. the third row in the above table. </p>
  
  <p>The tables are very large, so I would prefer to use SELECT statements rather than DELETE or ALTER which seem to be slow.</p>
  
  <p>Any help much appreciated!</p>