Question

I’m creating a table that has a basisId field as the primary key. There’s also another field parentBasis which would be a reference to another tuple with that.basisId equal to this.parentBasis. What I want to do to is express this constraint while creating the table.

Something like: ADD CONSTRAINT CHECK EXISTS this.parentBasis AS somewhere.basisId (Obviously not real MySQL).

A quick browse through the MySQL dev pages didn’t do much good. Any help would be appreciated.

Thanks.

Answer 1

If you’re using InnoDB then you can create a foreign key from the table to itself. For example:

create table t (
    id int not null primary key,
    parent int null
);
alter table t add constraint foreign key (parent) references t(id);

then t.parent would either have to be NULL or a t.id value.