5 ms·

Why shouldn't the "sum" of an empty set return 'NULL'? I could understand why a 'count' of an empty set should be 0 (which it is in SQL Server).

• eurleif 13y ago
  sum(A) + sum(B) = sum(A ∪ B) sum(A) + sum({}) = sum(A ∪ {}) sum(A) + sum({}) = sum(A) sum({}) = 0
  • dbaupp 13y ago
    (This assumes either A and B are multisets, or they are disjoint.)
    • kragen 13y ago
      Indeed, but in the context of minor changes in how things SQL should behave, we can assume that everything is a multiset.