On Mon, Feb 10, 2025 at 9:32 AM Tomas Vondra <to...@vondra.me> wrote: > E.g. imagine we have a join of 8 relations, with F (fact), dimensions D1 > and D2, and then some artibrary tables T1, T2, T3, T4, T5. And let's say > deconstruct_recurse() sees them in this particular order > > [F, T1, T2, D1, D2, T3, T4, T5] > > AFAICS doing something in deconstruct_recurse() would likely split the > joinlist into four parts > > [F, T1, T2] [D1] [D2] [T3, T4, T5] > > which does treat the D1,D2 as if join_collapse_limit=1, but it also > splits the remaining relations into two groups, when we'd probably want > something more like this: > > [F, T1, T2, T3, T4, T5] [D1] [D2] > > Which should be legal, because a requirement is that D1/D2 don't have > any other join restrictions (I guess this could be relaxed a bit to only > restrictions within that particular group).
Hmm, I'm still a little concerned about whether the resulting joins are legal. Suppose we have a join pattern like the one below. F left join (D1 inner join T on true) on F.b = D1.b left join D2 on F.c = D2.c; For this query, the original joinlist is [F, D1, T, D2]. If we reorder it to [[F, T], D1, D2], the sub-joinlist [F, T] would fail to produce any joins, as the F/T join is not legal. This may not be the pattern we are targeting. But if we intend to support it, I think we need a way to ensure that the resulting joins are legal. Thanks Richard
