title: How to SUM multiple DECODE values?
body: <p>I have the following decodes in my SELECT case:</p>
  
  <pre><code>DECODE (table_name, 'RECHNUNG', SUM(beleg_betrag_offen) ) as re_be_of,
  DECODE (table_name, 'GUTSCHRIFT', SUM(beleg_betrag_offen) ) as gs_be_of,
  DECODE (table_name, 'ZAHLUNG', SUM(beleg_betrag_offen) ) as za_be_of
  </code></pre>
  
  <p>I want to add up those 3 values (every DECODE has always some results) but I can't. When I write a simple</p>
  
  <pre><code>re_be_of + gs_be_of + za_be_of
  </code></pre>
  
  <p>I don't even see any result. Does anyone know where my mistake is?</p>