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Good article. Another one that I find counter intuitive is that the sum of an empty set returns null which goes against set theory (states it should return 0)

Good article. Another one that I find counter intuitive is that the sum of an empty set returns null which goes against set theory (states it should return 0) but apparently this is by design

aeorgnoieang 13y ago
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.