On Wed, Mar 31, 2021, at 22:25, Isaac Morland wrote: > > Maybe I have a different proposal in mind than anybody else, but I don't > think there is a problem with multiple joins to the same table. If the joins > are via the same constraint, then a single join is enough, and if they are > via different constraints, the constraints have unique names. > > I think if TA is a table with a foreign key constraint CB to another table > TB, then the hypothetical expression: > > TA -> CB > > really just means: > > (select TB from TB where (TB.[primary key columns) = (TA.[source columns of > constraint CB])) > > You can then add .fieldname to get the required fieldname. The issue is that > writing it this way is hopelessly verbose, but the short form is fine. The > query planner also needs to be guaranteed to collapse multiple references > through the same constraint to a single actual join (and then take all the > multiple fields requested). > > If TA is a table with a foreign key constraint CB to TB, which has a foreign > key constraint CC to TC, then this expression: > > TA -> CB -> CC > > just means, by the same definition (except I won't expand it fully, only one > level): > > (select TC from TC where (TC.[primary key columns) = ((TA -> CB).[source > columns of constraint CC])) > > Which reminds me, I often find myself wanting to write something like a.(f1, > f2, f3) = b.(f1, f2, f3) rather than (a.f1, a.f2, a.f3) = (b.f1, b.f2, b.f3). > But that's another story
Maybe “anonymous join” would be a good name for this, similar to anonymous functions. The joined table(s) would not pollute the namespace. /Joel
