title: Combine two columns in one column
body: <p>I have column 1 and column 2, and want to combine them into column 3 of the same table. If the column 2 is null then display column 1 value, if column 1 is null, them display column 2 data. If both of them are null, then display null. I tried two things:</p>
  
  <p>1) using CONCAT
  <code>SELECT CONCAT(Column1, Column2) AS Column3 FROM TEST_ATTRIBUTES</code>.</p>
  
  <p>It just merges the columns only when both of them are not null. otherwise it just prins null.</p>
  
  <p>2) using (column1 + column 2).</p>
  
  <p><code>SELECT (Column1 + Column2) AS Column3 FROM TEST_ATTRIBUTES</code>.</p>
  
  <p>doesn't show desired output.</p>
  
  <p>I'm writing this code in java.
  Thanks</p>