Query below returns number of tables that don't have foreign keys and are not referenced by other tables with foreign keys.

This diagram illustrates Loner Tables concept:

Query

select count(distinct tab.table_schema || '.' || tab.table_name) as tables,
       count(distinct tab.table_schema || '.' || tab.table_name)
            - count(distinct rel.table_schema || '.' || rel.table_name)
            as loner_tables,
       round(100.0*(count(distinct tab.table_schema || '.' || tab.table_name)
            - count(distinct rel.table_schema || '.' || rel.table_name))
            /count(distinct tab.table_schema || '.' || tab.table_name),2) || '%'
            as loner_ratio
from information_schema.tables tab
left join (
          select distinct tco.table_schema ,tco.table_name 
          from information_schema.referential_constraints rco
          join information_schema.table_constraints tco 
               on rco.unique_constraint_name = tco.constraint_name
               and rco.unique_constraint_schema = tco.table_schema
          union all
          select distinct tco.table_schema, tco.table_name 
          from information_schema.referential_constraints rco
          join information_schema.table_constraints tco 
               on rco.constraint_name = tco.constraint_name
               and rco.constraint_schema = tco.table_schema
) rel on rel.table_name = tab.table_name 
    and rel.table_schema = tab.table_schema
where tab.table_schema not in ('information_schema', 'pg_catalog') 
      and tab.table_type ='BASE TABLE';

Columns

• tables - number of tables in database
• loner_tables - number of Loner Tables
• loner_ratio - Loner Ratio - % of Loner Tables

Rows

• Scope of rows: query returns one row

Sample results