Get all constraints of a PostgreSQL table

get_table_constraints.sql

SELECT con.*
    FROM pg_catalog.pg_constraint con
        INNER JOIN pg_catalog.pg_class rel
            ON rel.oid = con.conrelid
        INNER JOIN pg_catalog.pg_namespace nsp
            ON nsp.oid = connamespace
    WHERE nsp.nspname = '<schema name>'
        AND rel.relname = '<table name>';