> -----Original Message----- > From: Merlin Moncure [mailto:mmoncure@xxxxxxxxx] > Sent: Friday, October 28, 2011 8:29 PM > To: Dmitry Epstein > Cc: tgl@xxxxxxxxxxxxx; pgsql-general@xxxxxxxxxxxxxx; Peter Gagarinov > Subject: Re: nextval skips values between consecutive calls > > On Fri, Oct 28, 2011 at 10:28 AM, <depstein@xxxxxxxxxxxxxxxxx> wrote: > >> -----Original Message----- > >> From: Tom Lane [mailto:tgl@xxxxxxxxxxxxx] > >> Sent: Friday, October 28, 2011 7:22 PM > >> To: Dmitry Epstein > >> Cc: pgsql-general@xxxxxxxxxxxxxx; Peter Gagarinov > >> Subject: Re: nextval skips values between consecutive calls > >> > >> <depstein@xxxxxxxxxxxxxxxxx> writes: > >> > -- This is rather surprising > >> > select nextval(' test_sequence'), generate_series(1, 1); -- 3, 1 > >> > select nextval(' test_sequence'), generate_series(1, 1); -- 5, 1 > >> > >> > Is there any explanation for why nextval skips a value in the second > case? > >> > >> The targetlist is evaluated twice because of the presence of the > >> set-returning function. On the second pass, generate_series reports > >> that it's done, and so evaluation stops ... but nextval() was already called a > second time. > >> > >> SRFs in SELECT targetlists are a pretty dangerous thing, with a lot > >> of surprising behaviors, especially if you combine them with other > >> volatile functions. I recommend avoiding them. They'll probably be > >> deprecated altogether as soon as we have LATERAL. > >> > >> regards, tom lane > > > > What's a good alternative in the meantime? Suppose I need to > > incorporate some unnests into my select, for example? (Well, I already > > found one alternative that seems to work, but I am not sure that's > > optimal.) > > Typically for guaranteed LATERAL-like behaviors you need to use a CTE. > > merlin What's a CTE? -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
