Postgres: SQL to list table foreign keys

Question

Is there a way using SQL to list all foreign keys for a given table? I know the table name / schema and I can plug that in.

Answer 1

You can use the PostgreSQL system catalogs. Maybe you can query pg_constraint to ask for foreign keys. You can also use the Information Schema

Answer 2

You can do this via the information_schema tables. For example:

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 table_name='mytable';

Answer 3

psql does this, and if you start psql with:

psql -E

it will show you exactly what query is executed. In the case of finding foreign keys, it's:

SELECT conname,
  pg_catalog.pg_get_constraintdef(r.oid, true) as condef
FROM pg_catalog.pg_constraint r
WHERE r.conrelid = '16485' AND r.contype = 'f' ORDER BY 1

In this case, 16485 is the oid of the table I'm looking at - you can get that one by just casting your tablename to regclass like:

WHERE r.conrelid = 'mytable'::regclass

Answer 4

I created little tool to query and then compare database schema: Dump PostgreSQL db schema to text

There is info about FK, but ollyc response gives more details.