A-ha, interesting ! I think we have some specific use cases where it'd be worth the overhead, I'd need to measure it, though;
Do you think there'd be room to accept a contribution for such functionality with a disabled-by-default pg setting, or are you skeptical it would ever be worth the trade-off ? Thanks again, Danny On Thu, Aug 4, 2022 at 4:38 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > Danny Shemesh <dany...@gmail.com> writes: > > That is of course correct, but what I mean is that, I think that if one > > would explicitly query f(x), and never for x directly, it would've been > > theoretically possible to say that the index is covering for every f(x), > > wouldn't it ? > > Theoretically, yeah, but we don't support that: an index-only scan > will only be considered if x itself is available from the index. > There are a couple of reasons for that, but the main one is that > detecting whether an index matches the query would be far more expensive > if it had to consider expression subtrees not just the base Vars. > > regards, tom lane >
