Re: Storage of Foreign Keys

On Mon, Sep 21, 2009 at 11:09 AM, Alan Hodgson <ahodgson@simkin.ca> wrote:
> On Monday 21 September 2009, Christian Koetschan
> <c.koetschan@biozentrum.uni-wuerzburg.de> wrote:
>> Is everything I insert into mycolA and mycolB stored twice, or
>> is there something like a pointer/reference from mycolA to the things
>> stored in mycolB?
>>
>
> It's stored twice and for performance you need to index it in both tables.
> If you put ON UPDATE CASCADE on it, an update to the master will hit both
> tables though.

Slight correction.  You might need to index it on both ends for
performance.  There are some instances where the referencing table
only ever has a few rows in it, and in those cases, you likely don't
need an index.