> On 8 Jun 2021, at 22:50, Thomas Kellerer <sham...@gmx.net> wrote: > > Marc Millas schrieb am 03.06.2021 um 22:51: >> on a table we need a primary key and to get a unique combinaison, we need 3 >> columns of that table: >> 1 of type integer, >> 1 of type text, >> 1 of type geometry >> > > How do you define the "uniqueness" of the geometry?
That is actually the big question here. Multiple “unique” geometries can specify the same geometry! A geom as simple as a line from (0,0) - (1,0) can just as easily be specified as (1,0) - (0,0). That’s the simplest case, and one could argue that the point of origin is different, but the next example would be a triangle starting at the same origin but traversed in different directions. It gets harder the more vertices a polygon has. I would argue that a geometry type is ill-suited as a primary key column candidate. Now, of course, the OP could have a case where their geometries are guaranteed to be unique regardless, but they’d better make sure before adding them to the PK. Alban Hertroys -- If you can't see the forest for the trees, cut the trees and you'll find there is no forest.
