Hello, I'm not a C coder and can't help....but I *love* cross-tab/pivot tables. They're the best, and just fantastic for preparing data to feed into various analysis tools. The tablefunc module is helpful, but a bit awkward to use (as I remember it.)
>From a user's point of view, I high-performance cross-tab generator would be just fantastic. As I understand it, this is what's involved in a pivot: 1. Identify rows that should be *grouped* (consolidated.) 2. Distinguish the value that identifies each *derived* column. 3. Distinguish the value that *identifies* each row-column value. 4. *Collapse* the rows, *build* the columns, and *populate* the 'cells' with data. In an ideal world, you would be able to perform different grouping operations. Such as count, sum, avg, etc. If there's a way to do this in a system-wide and standards-pointing way, so much the better. *Apologies* if I'm violating list etiquette by jumping in here. I've been lurking on several Postgres lists for a bit and picking up interesting details every day. If I've been Unintentionally and Cluelessly Off, I'm find with being told. On Sat, Jan 26, 2019 at 10:49 AM David Fetter <da...@fetter.org> wrote: > On Fri, Jan 25, 2019 at 04:31:00PM -0600, Merlin Moncure wrote: > > On Fri, Jan 25, 2019 at 3:16 PM David Fetter <da...@fetter.org> wrote: > > > > > > 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. > > > > Interesting. Do you see that the spec (it makes my brain hurt) can > > handle that kind of repivoting? > > I believe the constructs can nest and/or refer to each other, so yes. > > 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 > >
