> -----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.) Dmitry Epstein | Developer Allied Testing www.alliedtesting.com We Deliver Quality. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
