title: How I can use variable as field name in plpgsql
body: <p>It is possible to make something like this in Postgres?</p>
  
  <pre><code>DECLARE variable VARCHAR  
  BEGIN  
      variable := TG_RELNAME || '_id';  
      OLD.variable = 123;  
  END;
  </code></pre>
  
  <p>I can't use value of variable as field_name...</p>
  
  <p>p.s. my version of db is 8.4.</p>