On Monday 12 June 2006 12:10, Jo wrote:
> Kern Sibbald wrote:
> > Basing "consecutiveness" on MediaId will not work very well as the SQL
> > gurus can confirm since the MediaIds are not guaranteed to be
> > consecutive. In fact, if you ever delete any volumes, in most SQL
> > engines (e.g. like MySQL), the next volume created will take on the
> > lowest free MediaId.
>
> I'm pretty sure that the normal way of working for an SQL engine is to
> always use a higher number when creating new records. That's how the
> serial type in PostgreSQL works. I don't think an RDBMS tries to
> 'recycle' primary keys. This might have very nasty side effects when
> there would still be some foreign keys point to that primary key. Of
> course, I don't know if this MediaID is in fact a primary key.
Using the next higher key number may be how PostgreSQL does it, but I would
hesitate to call this "the normal way of working" since there are probably
many more MySQL installations, and I can assure you that MySQL has no problem
reassigning a previously used ID at least when using the MyISAM indexes as I
am.
In any case, what is "normal" is not very important. What counts is that you
can never be 100% sure how the ID will be assigned since it is up to the DB
to decide, and to the best of my knowledge there is no external standard that
requires anything one way or another.
--
Best regards,
Kern
(">
/\
V_V
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