SELECT s.schema_name AS schema, COUNT(tc.table_schema) AS number_of_foreign_keys 
FROM information_schema.schemata AS s LEFT JOIN 
(SELECT table_schema
FROM information_schema.table_constraints 
WHERE constraint_type = 'FOREIGN KEY') AS tc ON s.schema_name=tc.table_schema
WHERE schema_name NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
GROUP BY s.schema_name
ORDER BY COUNT(tc.table_schema) DESC, s.schema_name;