title: Union of two arrays in PostgreSQL without unnesting
body: <p>I have two arrays in PostgreSQL that I need to union. For example:</p>
  
  <p><code>{1,2,3}</code> union <code>{1,4,5}</code> would return <code>{1,2,3,4,5}</code></p>
  
  <p>Using the concatenate (||) operator would not remove duplicate entries, i.e. it returns <code>{1,2,3,1,4,5}</code></p>
  
  <p>I found one solution on the web, however I do not like how it needs to unnest both arrays:
  <code>select ARRAY(select unnest(ARRAY[1,2,3]) as a UNION select unnest(ARRAY[2,3,4,5]) as a)</code></p>
  
  <p>Is there an operator or built-in function that will cleanly union two arrays?</p>