PostGres support

Drupal 6.11 with postgreSQL and usage of postgres schema

Text moved to drupal core issues, now here: #459134: Contribution: Drupal 6.11 with postgreSQL and usage of postgres schema

When migrating data from external PostGres database to default Drupal's Postgres database, I get the following error:
ERROR: schema "drup" does not exist query: SELECT document.document_id AS document_id, div_document.document_id AS div_document_document_id, document.date_created AS document_date_created, document.website_id AS document_website_id, document.date_rel AS document_date_rel, document.locale AS document_locale, document.date_modified AS document_date_modified, document.seq AS document_seq, document.status AS document_status, document.head AS document_head, document.subhead AS document_subhead, document.author AS document_author, document.annotation AS document_annotation, document.ref_email AS document_ref_email, document.picture AS document_picture, document.ref_url AS document_ref_url, document.announce AS document_announce, document.created_by AS document_created_by, document.modified_by AS document_modified_by, document.doc_alias AS document_doc_alias, source.source_id AS source_source_id, document.priority AS document_priority, document.introduction AS document_introduction, graphics.filename AS graphics_filename, textdata.text AS textdata_text FROM document document LEFT JOIN div_document div_document ON document.document_id = div_document.document_id LEFT JOIN source source ON document.source_id = source.source_id LEFT JOIN graphics graphics ON document.picture = graphics.filename LEFT JOIN textdata textdata ON document.document_id = textdata.document_id LEFT JOIN drup.document_map document_map ON document.document_id = document_map.sourceid LEFT JOIN drup.document_msgs document_msgs ON document.document_id = document_msgs.sourceid WHERE (document_map.sourceid IS NULL) AND (document_msgs.sourceid IS NULL) LIMIT 5 OFFSET 0 in /var/www/dru.polit/htdocs/sites/all/modules/migrate/migrate.module on line 400.
AFAICS Postgres does not support at all queries involving multiple databases. I HAVE TO use a different schema in the default database to achieve what I wanted. Also, I think one can hit this error when trying to import data from Postgres to a mysql-based Drupal installation. I suppose the right way to deal with it is to use just one database per query, probably doing these joins in PHP (yes I understand this is cruel) or first importing data to default database and then doing the joins.

Postgres can join across schemas within a database. But Migrate module, for example, can't import data from postgres to mysql or vice versa (not only between two Postgres databases) because of such statement usage. So, I think this is worth fixing or at least noticing in the documentation.