Re: all foreign key should have index?

Gene Wirchenko wrote:

> On Wed, 1 Feb 2006 20:17:11 +0000 (UTC), "Murdoc"
> <murdoc_0_at_hotmail.com> wrote:
>
> > Gene Wirchenko wrote:
> >
> >> On Tue, 31 Jan 2006 22:12:56 +0000, Eric Junkermann
> >> <eric_at_deptj.demon.co.uk> wrote:
> >>
> >> [snip]
> >>
> >> > When you delete a parent row, or update its key, the DBMS needs to find
> >> > the children, either to cascade the operation or to forbid it - how can
> >> > it do this efficiently without an index? But of course if you never do
> >> > those things,
> >> > you might still need it to find child rows efficiently anyway.
> >>
> >> Why does it have to be an index?
>
> > Generally: efficiency. If you want the DB to enforce referential integrity, the operation of
> > doing so needs to be efficient. A search of the entire 'FK' table to ensure that a record can
> > be deleted from the 'PK' table is (a) inefficient; and (b) pointless. Or even worse, on a
> > cascade delete. The search (when using an index) really comes down to "Is there an entry in the
> > index for this field value?".
> >
> > Again, it does come down to the size of the table. A table with a maximum of about 10 rows is
> > not going to have a large performance gain with an index (or maybe a performance detriment).
>
> That is not the point. Why does it have to be an INDEX?
>
> You have been assuming that an index is the only way. It is not.

Then what is the other way? What other mechanism allows efficient searching of a table without a full search?

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