Why is 'use_alias' hardcoded to true in deparseFromExprForRel() for some cases - Mailing list pgsql-hackers

In the postgrs_fdw deparser code, deparseFromExprForRel() appends an alias to the remote query based on the 'use_alias' boolean flag.

For a simple query, 'use_alias' is determined by `bms_membership(scanrel->relids) == BMS_MULTIPLE` condition. Example: https://github.com/postgres/postgres/blob/master/contrib/postgres_fdw/deparse.c#L1385C2-L1388

But for JOINs, 'use_alias' is always hardcoded to true. Examples:

1. https://github.com/postgres/postgres/blob/master/contrib/postgres_fdw/deparse.c#L2067-L2069

2. https://github.com/postgres/postgres/blob/master/contrib/postgres_fdw/deparse.c#L2336-L2337

3. https://github.com/postgres/postgres/blob/master/contrib/postgres_fdw/deparse.c#L2419-L2420

This seems like an extra-protection in case of joins. But it could happen that the join is across 2 different foreign postgres-servers (means each foreign server will do SCAN only, and the JOIN will happen at the upper layer). In that case, using aliases in the remote queries seem redundant to me.

Please correct me if I am missing something. Can we note pass `bms_membership(foreignrel->relids) == BMS_MULTIPLE` instead?