title: SQL server average when first value 0
body: <p>How to get average with this query? Query works fine but I can't get average of all columns</p>
  
  <pre><code> INSERT INTO db_name(
      AVERAGE_WEIGHT,
      RUNNING_TOTAL,
      ROLLING_AVERAGE)
      VALUES
      (onvert(real, '515,
      (convert(real, '515 + (SELECT SUM(average_weight)  FROM db_name)),
      (SELECT AVG(average_weight)  FROM db_name))
  
  AVERAGE_WEIGHT    RUNNING_TOTAL     ROLLING_AVERAGE
  515            NULL                  NULL
  510            1025                  515
  500            1525                  512.2
  </code></pre>
  
  <p>My last Column should be NULL, 512.2, 508.33 How to get right values? It is possible?</p>