Обсуждение: Cross DB query
A question I always have, and I didn´t find anybody answering it. If it´s possible
select * from MyDB.MySchema.MyTable;
And from user point of view ... all databases are accessible for the same postgres instance, user just says connect to this or that database, why is it not possible to do
select * from FirstDB.FirstSchema.FirstTable join SecondDB.SecondSchema. SecondTable;
Everything I found was how to connect, using FDW or DBLink, but not why.
regards,
Marcos
On Wednesday, December 8, 2021, Marcos Pegoraro <marcos@f10.com.br> wrote:
A question I always have, and I didn´t find anybody answering it. If it´s possibleselect * from MyDB.MySchema.MyTable;
No, if you specify MyDB is must match the database you’ve chosen to log into.
Everything I found was how to connect, using FDW or DBLink, but not why.
Because someone decades ago made that decision and all of the internals rely upon it, making a change cost prohibitive. In short, we allow the syntax because that standard says we should but its not very useful beyond that.
I’m pretty sure I’ve seen this in the documentation but a quick glance didn’t turn it up. Experimentation does prove that it works in this manner though.
David J.