Question

I have a country and let’s say user tables, and in case a submitted country does not match a constraint I want a null go there instead.

create table countries(
    ccode char(2), primary key (ccode)
);

create table users(
    ccode char(2), foreign key (ccode) references countries(ccode)
);

insert into countries values('ru'),('us'),('hk');

Now if the user submitted an nonexistent code, eg:

insert into users values('xx');

• The query would actually fail due to the fk constaint. But I want it to write a null instead. How can we do this?

Answer 1

Answering my own question it looks like this is the way to do it:

(But if you suggest a better answer I will accept it of course)

insert into users values((select ccode from countries where ccode='x'));

^ This will return a code, and a null if it didn’t match – which is what I want.