SELECT pg_size_pretty( pg_database_size('test_db1') ) as db_size;

SELECT schema_name, 
       pg_size_pretty(sum(table_size)) as schema_size,
       cast((sum(table_size) / database_size) * 100 as DECIMAL(18,2)) as percentage
FROM (
  SELECT pg_catalog.pg_namespace.nspname as schema_name,
         pg_relation_size(pg_catalog.pg_class.oid) as table_size,
         sum(pg_relation_size(pg_catalog.pg_class.oid)) over () as database_size
  FROM   pg_catalog.pg_class
     JOIN pg_catalog.pg_namespace ON relnamespace = pg_catalog.pg_namespace.oid
) t
GROUP BY schema_name, database_size;

SELECT pg_size_pretty(pg_relation_size('public.test')) as table_size FROM pg_tables LIMIT 1;
-- or SELECT pg_size_pretty( pg_total_relation_size('test') ) as table_size;

SELECT relname, nspname, pg_size_pretty(pg_relation_size('"' || relname || '"')) as table_size
FROM pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace  
WHERE c.relkind IN ('r','') AND n.nspname NOT IN ('pg_catalog', 'pg_toast') AND pg_table_is_visible(c.oid) 
AND nspname = 'public'
ORDER BY c.relpages DESC;

SELECT  'id' AS column_name
        ,sum(pg_column_size('id')) AS total_size
        ,CAST(avg(pg_column_size('id')) AS DECIMAL(18,2)) AS average_size
        ,CAST(sum(pg_column_size('id')) * 100.0 / PG_RELATION_SIZE('public.test') AS DECIMAL(18,2)) AS percentage
FROM    public.test
;

SELECT
    tc.table_schema, 
    tc.constraint_name, 
    tc.table_name, 
    tc.constraint_type,
    kcu.column_name, 
    ccu.table_schema AS foreign_table_schema,
    ccu.table_name AS foreign_table_name,
    ccu.column_name AS foreign_column_name 
FROM information_schema.table_constraints AS tc 
JOIN information_schema.key_column_usage AS kcu
    ON tc.constraint_name = kcu.constraint_name
    AND tc.table_schema = kcu.table_schema
JOIN information_schema.constraint_column_usage AS ccu
    ON ccu.constraint_name = tc.constraint_name
WHERE (tc.constraint_type = 'FOREIGN KEY' OR tc.constraint_type = 'PRIMARY KEY')
    AND tc.table_schema='public'
    AND tc.table_name='test';

SELECT 
    c.relnamespace::regnamespace AS schema_name,
    c.relname AS table_name,
    i.indexrelid::regclass AS index_name,
    i.indisprimary AS is_pk,
    i.indisunique AS is_unique
FROM pg_index i
JOIN pg_class c ON c.oid = i.indrelid
WHERE c.relname = 'test';

SELECT grantee
FROM   information_schema.table_privileges 
WHERE table_schema = 'public' AND table_name = 'test' AND  privilege_type = 'DELETE';