On Fri, Jan 25, 2019 at 02:21:55PM -0600, Merlin Moncure wrote: > Hackers, > > We have a strong need to make a variant to the crosstab interface so > that data that is pivoted one way would be sent through a crosstab > like function so that it would be pivoted another way. For example, > if you had > > row 0: a1, a2, a3, k1, c1, c2, ... > row 1: a1, a2, a3, k2, c1, c2, ... > row 2: a1, a2, a3, k3, c1, c2, ... > ... > > where 'a' columns are uninteresting attribute columns, 'k' is the > dimension we want to pivot on, and c1->cN would be stacked vertically, > so that we'd end up with, > row 0: a1, a2, a3, c1, k1, k2, ... > row 1: a1, a2, a3, c2, k1, k2, ... > row 2: a1, a2, a3, c3, k1, k2, ... > > There are various SQL level approaches to this but they tend to be > imperformant with large datasets so that I think a crosstab-like C > implementation ought to be able to do better (or at least I hope so) > since you have to cross product rows and columns in such a way that > you can get a clean join. Cribbing from tablefunc.c I don't think > this is a terrible challenge to do in hash table style. > > Questions on the table: > *) Has anyone done anything like this or know of any current implementations? > *) Would there be any interest in expanding tablefunc along these lines?
There's something in SQL:2016 that I read as crosstabs, or at least as enabling crosstabs. https://www.iso.org/standard/69776.html If we're going to put work into crosstabs, it seems to me that the "we" needs to be the project as a whole, and the work should be, to the extent reasonable, toward standard compliance. Best, David. -- David Fetter <david(at)fetter(dot)org> http://fetter.org/ Phone: +1 415 235 3778 Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate
