[HACKERS] Behavior of OFFSET -1
Before 9.3, you got an error from this: regression=# select * from tenk1 offset -1; ERROR: OFFSET must not be negative But 9.3 and up ignore the negative OFFSET. This seems to be a thinko in my commit 1a1832eb. limit_needed() thinks it can discard the Limit plan node altogether, which of course prevents nodeLimit.c from complaining: /* Executor would treat less-than-zero same as zero */ if (offset 0) return true;/* OFFSET with a positive value */ I don't recall the reasoning behind that comment for sure, but I imagine I examined the behavior of ExecLimit() and failed to notice that there was an error check in recompute_limits(). This seems to me to be a clear bug: we should reinstate the former behavior by tightening this check so it only discards OFFSET with a constant value of exactly 0. Anyone think differently? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Behavior of OFFSET -1
On Tue, Jul 22, 2014 at 12:49 PM, Tom Lane t...@sss.pgh.pa.us wrote: Before 9.3, you got an error from this: regression=# select * from tenk1 offset -1; ERROR: OFFSET must not be negative But 9.3 and up ignore the negative OFFSET. This seems to be a thinko in my commit 1a1832eb. limit_needed() thinks it can discard the Limit plan node altogether, which of course prevents nodeLimit.c from complaining: /* Executor would treat less-than-zero same as zero */ if (offset 0) return true;/* OFFSET with a positive value */ I don't recall the reasoning behind that comment for sure, but I imagine I examined the behavior of ExecLimit() and failed to notice that there was an error check in recompute_limits(). This seems to me to be a clear bug: we should reinstate the former behavior by tightening this check so it only discards OFFSET with a constant value of exactly 0. Anyone think differently? Not I. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Behavior of OFFSET -1
On Tue, Jul 22, 2014 at 12:49:37PM -0400, Tom Lane wrote: Before 9.3, you got an error from this: regression=# select * from tenk1 offset -1; ERROR: OFFSET must not be negative That seems eminently sane, and should continue to error out, IM. The only circumstance I can imagine where this could be argued not to be is just casuistry, namely LIMIT m OFFSET -n might be argued to mean LIMIT m-n. Cheers, David. -- David Fetter da...@fetter.org http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: david.fet...@gmail.com iCal: webcal://www.tripit.com/feed/ical/people/david74/tripit.ics Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
