Thanks a lot, Jeff!
On Wed, Nov 14, 2012 at 11:59 AM, Jeff Janes <jeff.ja...@gmail.com> wrote: > On Wed, Nov 14, 2012 at 12:12 AM, Tianyin Xu <t...@cs.ucsd.edu> wrote: > > Hi, Postgresql, > > > > I want to understand how the query optimizers affect the output of the > > window functions. > > Use "EXPLAIN". > > One is an index scan, one is a bitmap scan. They return rows in a > different order. > > .. > > > I don't understand why the results are different. Intuitively, the > queries > > show return the same results no matter what plan the optimizer choose. > > My intuition is that the query should refuse to run at all, because > the results are order dependent and you haven't specified an ordering. > > What do you mean by "refused to run"? You mean we have to specify the order when using the window functions? Could you explain more? Thanks! > Cheers, > > Jeff > -- Tianyin XU, http://cseweb.ucsd.edu/~tixu/
