How to Add Check Constraint between Tables (or change DDL)? Given the following PostgreSQL table definitions:

postgres=# create table if not exists messages(
postgres(#     id serial primary key, 
postgres(#     max_length smallint not null check (max_length &gt; 0),
postgres(#     default_text text check (length(default_text) &lt;= max_length),
postgres(#     created_on timestamp with time zone not null
postgres(# );
CREATE TABLE
postgres=# 
postgres=# create table if not exists customized_messages(
postgres(#     message_id serial references messages(id) not null,
postgres(#     message text not null, 
postgres(#     created_on timestamp with time zone not null
postgres(# );
CREATE TABLE


how can I enforce length(customized_messages.text) is &lt;= messages.max_length per the foreign key constraint?

Note that, as-is, I can do the following:

postgres=# insert into messages (id, max_length, default_text, created_on) values (1, 5, null, current_timestamp);
INSERT 0 1
postgres=# insert into customized_messages (message_id, message, created_on)  values (1, 'longer than 5', current_timestamp);
INSERT 0 1
postgres=# select * from messages;
 id | max_length | default_text |          created_on           
----+------------+--------------+-------------------------------
  1 |          5 |              | 2019-01-18 14:12:59.692075-05
(1 row)
postgres=# select * from customized_messages;
 message_id |    message    |          created_on           
------------+---------------+-------------------------------
          1 | longer than 5 | 2019-01-18 14:13:38.226987-05
(1 row)


So, I would like to not allow, e.g. check constraint or something else, the longer than 5 to be inserted since its length is &gt; 5.
One way is to duplicate the max_length column and enforce that they have identical values in the two tables with a composite foreign key (instead of the simple one):

create table if not exists messages(
    id serial
        primary key, 
    max_length smallint not null
        check (max_length &gt; 0),
    default_text text
        check (length(default_text) &lt;= max_length),
    created_on timestamp with time zone not null,
    unique (id, max_length)
);


create table if not exists customized_messages(
    message_id int not null,
    max_length smallint not null,
    message text not null
        check (length(message_text) &lt;= max_length), 
    created_on timestamp with time zone not null,
    foreign key (id, max_length)
        references messages (id, max_length)
);




Note (irrelevant to the question):  the message_id column in the 2nd table does not make sense to be serial and at the same time foreign key to the 1st table.