On Sun, Aug 5, 2012 at 1:21 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > Mike Christensen <mike@xxxxxxxxxxxxx> 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. Thanks Tom! That definitely makes sense.. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
