Jeff Janes <jeff.janes@xxxxxxxxx> writes: > On Mon, Jan 22, 2018 at 9:16 AM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: >> The point here is that that's an uncorrelated subselect --- ie, it >> contains no outer references --- so it need not be, and is not, >> re-evaluated at every outer row. > That seems rather circular. Why shouldn't a volatile be honored as > volatile just because it is in an uncorrelated sub-select? It is honored as volatile: it will be re-evaluated every time the sub-select is re-evaluated. It's just that there's no cause to re-evaluate the sub-select. I poked through the SQL standard to see if it spells out the semantics of uncorrelated subqueries anywhere, and couldn't find anything relevant at all. But this is how Postgres has understood the behavior of sub-selects for a very long time (~20 years). I'm pretty certain that there are people depending on it to behave this way. regards, tom lane
