title: Alias for using SELECT result in WHERE IN
body: <p>I have a query on which I use a WHERE IN SELECT. Here is the query:</p>
  
  <pre><code>SELECT tville_id, tville_nom, tville_etat
  FROM TAB_ZONE   
  INNER JOIN TAB_VILLES ON tville_id = tzone_cidade
  WHERE tzone_unidade1 = 1 
     OR tzone_unidade2 = 1 
     OR tzone_unidade3 = 1 
     OR tzone_unidade1 IN (SELECT tunidade_id FROM TAB_UNIDADE WHERE tunidade_parent = 1)
     OR tzone_unidade2 IN (SELECT tunidade_id FROM TAB_UNIDADE WHERE tunidade_parent = 1)
     OR tzone_unidade3 IN (SELECT tunidade_id FROM TAB_UNIDADE WHERE tunidade_parent = 1)
  ORDER BY tville_etat, tville_nom
  </code></pre>
  
  <p>It works, but as you can see I have three time the "SELECT tunidade_id" statement in the WHERE part. Is there a way to use the result of this SELECT  as an alias, so perform it only one time? (and is it usefull?)</p>
  
  <p>Thanks</p>