title: SQL: sum 3 columns when one column has a null value without replacing null with 0?
body: <p>Given table:</p>
  
  <pre><code>ID   ANOTHERID      ONE    TWO      THREE
  X1       B1          15    15       -
  X1       B2          10    -        - 
  X2       B1          -     20       -
  </code></pre>
  
  <p>This query:</p>
  
  <pre><code>SELECT SUM (ONE + TWO + THREE) FROM (TABLE)
  GROUP BY ID, ANOTHERID
  </code></pre>
  
  <p>I also tried</p>
  
  <pre><code>select sum(coalesce( ONE + TWO + THREE, ONE + TWO, ONE + THREE, ONE + 
  THREE))
  </code></pre>
  
  <p>at least one column has a null value. How can I still add them even if there is a null? As null and 0 have different meanings here (null means not started, 0 means not worked), I dont want to replace null with 0. Thanks</p>