Hi,
ok - I've checked.
> > > Why not? What's wrong with this:
> > >
> > > BORROWER
> > > BorrowerID
> > >
> > > BOOKS
> > > BookID
> > > BorrowerID (nullable)
> > >
> > > FK from Books.BorrowerID to Borrower.BorrowerID
> > >
> > > I haven't checked, but this _should_ be possible.
> > >
> > > With regards,
> >
> > Its a foreign key, you can not null foreign keys.. Thats the problem.
That's not true. Here's what I got:
CREATE TABLE inno1 (
PK_Col Integer NOT NULL DEFAULT 0,
Child_Col Integer,
PRIMARY KEY (
PK_Col
)
) TYPE=InnoDB ROW_FORMAT=fixed DEFAULT;
CREATE INDEX I_Inno1_ChildCol
ON inno1(Child_Col);
ALTER TABLE inno1 ADD FOREIGN KEY (Child_Col)
REFERENCES inno1 (PK_Col)
ON DELETE NO ACTION
ON UPDATE NO ACTION;
After that, I inserted data:
INSERT INTO inno1(PK_Col, Child_Col) VALUES (1, NULL);
INSERT INTO inno1(PK_Col, Child_Col) VALUES (2, NULL);
INSERT INTO inno1(PK_Col, Child_Col) VALUES (3, 1);
Now, can someone explain what the problem with NULLable FKs is?
With regards,
Martijn Tonies
Database Workbench - developer tool for InterBase, Firebird, MySQL & MS SQL
Server.
Upscene Productions
http://www.upscene.com
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