Mike Christensen <mike@kitchenpc.com> writes:
> 1) Is it possible to make int2 + int2 = int4?
We could do that, but why stop there? int4 + int4 can overflow, maybe
its result should be int8? int8 + int8 can overflow, maybe its result
should be numeric? numeric + numeric can overflow, now what? And what
about subtraction, multiplication, and various other operators?
The long and the short of it is that you've made an unwise choice of
datatype, if you have values that are close enough to the overflow
threshold for this to be an issue.
> 2) I've noticed if I have an index on (CookTime::Int4 +
> PrepTime::Int4), then the query WHERE (CookTime + PrepTime > 100)
> won't use the index. However, WHERE (CookTime::Int4 + PrepTime::Int4
> 100) *will* use the index. Is this by design, and can the query
> planner by smarter about this scenario?
Yes, and no. The planner does not know enough about the semantics of
cross-type coercions to infer that these expressions are equivalent.
In fact, they *aren't* equivalent, precisely because of the differing
prospects for overflow, and so the planner would be quite exceeding its
authority to replace one with the other.
regards, tom lane
