select only doc_id (#3920)

* select only doc_id

* select more doc ids

* fix user group

---------

Co-authored-by: Richard Kuo (Danswer) <rkuo@onyx.app>

backend/ee/onyx/db/user_group.py

@@ -218,14 +218,14 @@ def fetch_user_groups_for_user(
     return db_session.scalars(stmt).all()
 
 
-def construct_document_select_by_usergroup(
+def construct_document_id_select_by_usergroup(
     user_group_id: int,
 ) -> Select:
     """This returns a statement that should be executed using
     .yield_per() to minimize overhead. The primary consumers of this function
     are background processing task generators."""
     stmt = (
-        select(Document)
+        select(Document.id)
         .join(
             DocumentByConnectorCredentialPair,
             Document.id == DocumentByConnectorCredentialPair.id,