On Fri, Sep 2, 2016 at 9:11 AM, Andres Freund <and...@anarazel.de> wrote: > On 2016-09-02 09:05:35 -0500, Kevin Grittner wrote: >> On Fri, Sep 2, 2016 at 3:31 AM, Robert Haas <robertmh...@gmail.com> wrote: >>> On Tue, Aug 23, 2016 at 3:10 AM, Andres Freund <and...@anarazel.de> wrote: >> >>>> =# SELECT * FROM few, ROWS FROM(generate_series(1,3)); >>>> ┌────┬─────────────────┐ >>>> │ id │ generate_series │ >>>> ├────┼─────────────────┤ >>>> │ 1 │ 1 │ >>>> │ 2 │ 1 │ >>>> │ 1 │ 2 │ >>>> │ 2 │ 2 │ >>>> │ 1 │ 3 │ >>>> │ 2 │ 3 │ >>>> └────┴─────────────────┘ >>>> (6 rows) >>>> surely isn't what was intended. So the join order needs to be enforced. >>> >>> In general, we've been skeptical about giving any guarantees about >>> result ordering. > > Well, it's historically how we behaved for SRFs.
And until we had synchronized scans a sequential scan always returned rows in the order they were present in the heap. Implementation details are not guarantees. > I'm pretty sure that people will be confused if > SELECT generate_series(1, 10) FROM sometbl; > suddenly returns rows in an order that reverse from what > generate_series() returns. If this changes, it is probably worth a mentioning in the release notes. >> I think it is a very bad idea to move away from the statement that >> a query generates a set of rows, and that no order is guaranteed >> unless the top level has an ORDER BY clause. How hard is it to add >> ORDER BY 1, 2 to the above query? Let the optimizer notice when a >> node returns data in the needed order and skip the sort if possible. > > There's no such infrastructure for SRFS/ROWS FROM. Well, that's something to fix (or not), but not a justification for "except on Tuesdays when the moon is full" sorts of exceptions to simple rules about what to expect. No ORDER BY means no order guaranteed. -- Kevin Grittner EDB: 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
