Postgres check for foreign key

SELECT
    r.table_name
FROM information_schema.constraint_column_usage       u
INNER JOIN information_schema.referential_constraints fk
           ON u.constraint_catalog = fk.unique_constraint_catalog
               AND u.constraint_schema = fk.unique_constraint_schema
               AND u.constraint_name = fk.unique_constraint_name
INNER JOIN information_schema.key_column_usage        r
           ON r.constraint_catalog = fk.constraint_catalog
               AND r.constraint_schema = fk.constraint_schema
               AND r.constraint_name = fk.constraint_name
WHERE
    u.column_name = 'id' AND
    u.table_catalog = 'db_name' AND
    u.table_schema = 'public' AND
    u.table_name = 'table_a'

Source: stackoverflow.com

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