Re: Question on Structuring Product Attributes
Date: Mon, 17 Oct 2011 12:05:14 +0100
Message-ID: <slrnj9o2va.ghq.eric_at_teckel.deptj.eu>
On 2011-10-17, Derek Asirvadem <derek.asirvadem_at_gmail.com> wrote:
> On Oct 17, 5:25?am, Jonathan Leffler <jleff..._at_earthlink.net> wrote:
>>
>> Actually, Standard SQL does not support indexes at all. ?They are an
>> implementation detail that actual SQL DBMS use, but they are completely
>> outside the scope of the SQL standard.
>
> Sure. But let's not get side-tracked. (a) I am not writing a paper
> with fully qualified statements, I am responding to a post. (b) all
> SQLs [that are compliant with the standard and thus SQLs] have
> indices. Whether it is an Extension or not is not relevant to this
> thread, and I did not mean to imply that indices were standard, rather
> that all the SQLs have them, and have them in a visible column, non-
> pointer, form.
It's sort-of fun to watch two people who don't know enough trying to have an argument.
What on earth is "and have them in a visible column, non-pointer, form" supposed to mean? All you can ever see of an index (apart from its effect on query performance) is the list of columns indexed and some vendor-dependent stuff usually about physical storage.
>
> The point being argued is, Celko stated:
Just to pick on one more thing:
> - each PRIMARY KEY constraint builds an index
> - each UNIQUE constraint builds an index
Not "builds", but "usually needs" :
- nowhere is there a requirement that primary and unique keys be
implemented with an index
- only one index is needed and there is nothing to prevent an SQL parser
being smart enough to realise this
- if the parser is not smart enough there may well be a way of
second-guessing it and still ending up with only one index.
And finally...
> ... under the covers is not relevant ...
True, but you don't always seem to understand where the covers are.
Eric
-- ms fnd in a lbryReceived on Mon Oct 17 2011 - 13:05:14 CEST