Re: Can't create FOREIGN KEY restraints on InnoDb tables

* Andy Dustman
> On Mon, 2002-06-24 at 17:50, Roger Baklund wrote:
> > * andy@xxxxxxxxxxx
> > [...]
> > > The referred to keys are the same type and are indexed (they are
> > [...]
> > > CREATE TABLE genres (
> > >   genre_id        SMALLINT NOT NULL PRIMARY KEY,
> > [...]
> > >   genre_id        SMALLINT,
> >
> > ...does not look the same to me... ;)
>
> Ouch, you are correct, although they are the same *type*. However, this
> seems like a fairly severe restriction. Obviously a primary key must be
> NOT NULL, but there are certainly cases where a column which refers to a
> foreign key must be NULL. The docs do say that the foreign key
> constraints *can* have an ON DELETE SET NULL clause, which is
> meaningless if your column has to be set to NOT NULL due to referring to
> a primary key.

Yes, you are right, as Heikki pointed out in the previous message in this
thread.

> Perhaps this is only a deficiency, and not a bug, but the documentation
> could be a bit clearer on this. It says, "Corresponding columns in the
> foreign key and the referenced key must have similar internal data types
> inside InnoDB so that they can be compared without a type conversion."
> My understanding is that NOT NULL is only a column constraint and
> doesn't affect the data type.
>
> However... Even when I set the referring column to be SMALLINT NOT NULL,
> and create a new database, I still get the same error:
>
> ERROR 1005 at line 23: Can't create table './MP3d/tracks.frm' (errno:
> 150)

Like Heikki said: your problem is probably that you don't have indexes on
the foreign keys.

--
Roger
sql


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