Query below returns number of tables that have no foreign key constraint and are not referenced by any foreign key either. Tables like this we call Loner Tables.

Learn more about Loner Tables

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 != 'INFORMATION_SCHEMA'
      and tab.table_type ='BASE TABLE';

Columns

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

Rows

• Scope of rows: query returns one row

Sample results

Loner Ratio in our sample database is 13.64%, meaning that 13.64% of tables are not related to other tables.