Perhaps a unneccessary surrogate key

Copy SQL

with keys as (select 
(select nspname from pg_namespace where oid=c.relnamespace) as key_schema,
c.relname as key_table, 
c.oid as key_table_oid,
o.conkey AS key_col,
o.contype
from pg_constraint o inner join pg_class c on c.oid = o.conrelid
where o.contype in ('u','p') and cardinality(o.conkey)=1),
keys_unnest as (select key_schema, key_table, key_table_oid, key_col, key_col_num, ordin, contype
from keys, unnest(keys.key_col) with ordinality as k(key_col_num, ordin)),

keys_with_names AS (select key_schema, key_table, a_key.attname as key_col, contype
from keys_unnest k inner join pg_attribute a_key on k.key_col_num = a_key.attnum and k.key_table_oid = a_key.attrelid and a_key.attisdropped = false
),

fk as (select 
(select nspname from pg_namespace where oid=c.relnamespace) as key_schema,
c.relname as key_table, 
c.oid as key_table_oid,
o.conkey AS key_col
from pg_constraint o inner join pg_class c on c.oid = o.conrelid
where o.contype='f'),
fk_unnest as (select key_schema, key_table, key_table_oid, key_col, key_col_num, ordin
from fk, unnest(fk.key_col) with ordinality as k(key_col_num, ordin)),

fk_with_names AS (select key_schema, key_table, a_key.attname as key_col
from fk_unnest k inner join pg_attribute a_key on k.key_col_num = a_key.attnum and k.key_table_oid = a_key.attrelid and a_key.attisdropped = false),

ukey_not_fk AS (select key_schema, key_table, key_col
from keys_with_names
where contype='u'
except select key_schema, key_table, key_col
from fk_with_names)

SELECT c.table_schema, c.table_name , c.column_name
FROM information_schema.columns c
LEFT JOIN information_schema.domains d USING (domain_schema, domain_name)
INNER JOIN information_schema.schemata s
ON c.table_schema=s.schema_name
WHERE (coalesce (c.column_default, d.domain_default) ILIKE '%nextval%' OR c.is_identity='YES')
AND c.data_type IN ('smallint','integer','bigint')
AND (c.table_schema = 'public'
OR s.schema_owner<>'postgres')
AND EXISTS (SELECT *
FROM ukey_not_fk AS uk
WHERE uk.key_schema=c.table_schema
AND uk.key_table=c.table_name
AND uk.key_col=c.column_name)
AND EXISTS (SELECT *
FROM keys_with_names AS kn
WHERE kn.key_schema=c.table_schema
AND kn.key_table=c.table_name
AND kn.contype='p')

ORDER BY table_schema, table_name;