4 Replies Latest reply: Feb 17, 2014 1:05 PM by Srikanth P RSS

    Sum(A) + Sum(B) vs. Sum(A + B)

      We have a table consisting of:


      RowId - a unique identifier for each row

      A - any real number

      B - any real number


      There are a couple of ways to sum A and B together:


      • Sum(A) + Sum(B)
      • Sum(A + B)
      • Sum(Aggr(A + B, RowId))


      Sum(A + B) is equivalent to Sum(Aggr(A + B, RowId))


      When A or B can be NULL, Sum(A + B) is not equivalent to Sum(A) + Sum(B).


      Why? Because any calculation involving NULL will yield NULL!


      To take care of this, you can alter the field on load:

      IF(IsNull(A), 0, A) AS A


      Would there be any situations in which you need a metric to be NULL? If so, is there a way to treat NULL as 0 in Sum(A + B)?