multiple membership grants and information_schema.applicable_roles

I found that multiple membership grants added in v16 affects the 
information_schema.applicable_roles view.

Examples on a master, but they works for v16 too.

Setup multiple membership alice in bob:

postgres@postgres(17.0)=# \drg alice
                List of role grants
  Role name | Member of |   Options    | Grantor
-----------+-----------+--------------+----------
  alice     | bob       | INHERIT, SET | alice
  alice     | bob       | INHERIT, SET | charlie
  alice     | bob       | ADMIN        | postgres
(3 rows)

The application_roles view shows duplicates:

postgres@postgres(17.0)=# SELECT * FROM 
information_schema.applicable_roles WHERE grantee = 'alice';
  grantee | role_name | is_grantable
---------+-----------+--------------
  alice   | bob       | NO
  alice   | bob       | YES
(2 rows)

View definition:

postgres@postgres(17.0)=# \sv information_schema.applicable_roles
CREATE OR REPLACE VIEW information_schema.applicable_roles AS
  SELECT a.rolname::information_schema.sql_identifier AS grantee,
     b.rolname::information_schema.sql_identifier AS role_name,
         CASE
             WHEN m.admin_option THEN 'YES'::text
             ELSE 'NO'::text
         END::information_schema.yes_or_no AS is_grantable
    FROM ( SELECT pg_auth_members.member,
             pg_auth_members.roleid,
             pg_auth_members.admin_option
            FROM pg_auth_members
         UNION
          SELECT pg_database.datdba,
             pg_authid.oid,
             false
            FROM pg_database,
             pg_authid
           WHERE pg_database.datname = current_database() AND 
pg_authid.rolname = 'pg_database_owner'::name) m
      JOIN pg_authid a ON m.member = a.oid
      JOIN pg_authid b ON m.roleid = b.oid
   WHERE pg_has_role(a.oid, 'USAGE'::text);


I think that only one row with admin option should be returned.
This can be achieved by adding group by + bool_or to the inner select 
from pg_auth_members.

BEGIN;
BEGIN
postgres@postgres(17.0)=*# CREATE OR REPLACE VIEW 
information_schema.applicable_roles AS
SELECT a.rolname::information_schema.sql_identifier AS grantee,
     b.rolname::information_schema.sql_identifier AS role_name,
         CASE
             WHEN m.admin_option THEN 'YES'::text
             ELSE 'NO'::text
         END::information_schema.yes_or_no AS is_grantable
    FROM ( SELECT pg_auth_members.member,
             pg_auth_members.roleid,
             bool_or(pg_auth_members.admin_option) AS admin_option
            FROM pg_auth_members
            GROUP BY 1, 2
         UNION
          SELECT pg_database.datdba,
             pg_authid.oid,
             false
            FROM pg_database,
             pg_authid
           WHERE pg_database.datname = current_database() AND 
pg_authid.rolname = 'pg_database_owner'::name) m
      JOIN pg_authid a ON m.member = a.oid
      JOIN pg_authid b ON m.roleid = b.oid
   WHERE pg_has_role(a.oid, 'USAGE'::text);
CREATE VIEW
postgres@postgres(17.0)=*# SELECT * FROM 
information_schema.applicable_roles WHERE grantee = 'alice';
  grantee | role_name | is_grantable
---------+-----------+--------------
  alice   | bob       | YES
(1 row)

postgres@postgres(17.0)=*# ROLLBACK;
ROLLBACK

Should we add group by + bool_or to the applicable_roles view?

-- 
Pavel Luzanov
Postgres Professional: https://postgrespro.com