Question

Is there faster alternative to this:

Take almost 1 minute in our server.

SELECT
    tc.constraint_name, tc.table_name, kcu.column_name, 
    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
    JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name
WHERE constraint_type = 'FOREIGN KEY' AND tc.table_name='mytable';

Maybe using pg_class metadata?, thanks.

Answer 1

There is a problem: a foreign key can be on 2 or more columns (FOREIGN KEY (b, c) REFERENCES other_table (c1, c2)). You need to specify first, what to do with such keys.

Here is the query i use to get all the foreign keys, but it works correctly only for simple (one column) foreign keys.

SELECT pgcon.conname as constraint_name, 
       cast(pgcon.conrelid as regclass) as table_name,
       cast(pgcon.confrelid as regclass) as foreign_table_name,
       pga1.attname as column_name,
       pga2.attname as foreign_column_name
FROM pg_constraint pgcon
JOIN pg_attribute pga1 on (pgcon.conrelid = pga1.attrelid
                       and pga1.attnum = any(pgcon.conkey))
JOIN pg_attribute pga2 on (pgcon.confrelid = pga2.attrelid
                       and pga2.attnum = any(pgcon.confkey))
WHERE pgcon.conrelid = cast('table_name_here' as regclass)
  AND pgcon.contype = 'f'