具有相关表的条件约束

Question

I have a question related to SQL, more specifically to PostgreSQL. I'm currently trying to make some conditional constraints, and I have succeded in making a conditional constraint in a single table. In the example below, I want to make sure that the column cpf is not null only when the column client_type has the value "F".

CREATE TYPE client_type AS ENUM('F', 'J');

CREATE TABLE clients (
  id SERIAL NOT NULL UNIQUE, 
  name varchar(255), 
  client_type client_type NOT NULL, 
  cpf varchar(11), 
  cnpj varchar(14), 
  CHECK (CASE WHEN client_type = 'F' THEN cpf IS NOT NULL END), 
  CHECK (CASE WHEN client_type = 'J' THEN cnpj IS NOT NULL END)
);

My question is, it is possible to do that with related tables?

For instance: I have a table called aditional_info , that has a foreign key referencing to the clients table, and I want to enforce that some columns of the aditional_info table cannot be null only when the related row in the clients table have a column with the value "F".

I may be trying to do something that is impossible, so if someone could tell me if this is achievable in some way I'll be very grateful!

Answer 1

I was able to achieve what I was trying to do with a function. Don't know if this is the best approach, but so far it is working for me.

The function takes the client id, saves the client type into a variable and return it.

CREATE OR REPLACE FUNCTION checkClientType(int) RETURNS varchar as $$
DECLARE
    type varchar;
BEGIN
    SELECT client_type INTO type FROM clients WHERE id = $1;

    RETURN type;
END;
$$ LANGUAGE plpgsql;

Then I check if the value returned by the function is equal to "J", and if it is, I say that the municipal_registration column cannot be null.

CREATE TABLE aditional_info (
  id SERIAL NOT NULL UNIQUE,
  client_id int REFERENCES clients(id) ON DELETE SET NULL ON UPDATE CASCADE,
  rg varchar(10) NOT NULL,
  issuing_body varchar NOT NULL,
  birth_date timestamp NOT NULL,
  municipal_registration varchar,
  CONSTRAINT not_null_municipal_registration CHECK(CASE WHEN checkClientType(client_id) = 'J' THEN municipal_registration IS NOT NULL END)
);