Re: Fwd: Index on table when using DESC clause

God I love the sheer brilliance of that minus trick :-))
Tnx a lot

BTW: Are there any plans to change this kind of indexing behaviour ?
It makes no sense at all, and, it makes databases slow when you don't
know about this.

On 23 May 2005, at 23:15, Andrew Lazarus wrote:

> What you are trying to do makes perfect sense, but for some strange
> reason, Postgres doesn't like to do it. In a PG index, all of the
> columns are always stored in ascending order. So if you have an ORDER
> BY that is all ASC, it can start from the start of the index. And if
> you have an ORDER BY that is all DESC, it can start from the end. But
> if you want one column (like pages) DESC and the other (description)
> ASC, then PG will use a sequential scan or something else slow and
> stupid.
>
> Other RDBMS know how to do this, by supporting the
>
> CREATE INDEX foo ON bar(baz DESC, baz2 ASC)
>
> syntax. For PG, you need to fool it with an index on an expression, or
> a custom operator, or something. I once just made an extra column and
> used a trigger to be sure that -myvariable was in it at all times
> (-pages for you) and then made my index on the extra column. Since the
> extra column in ASC order is the same as the original in DESC, it
> works.
> <andrew.vcf>
Met vriendelijke groeten,
Bien à vous,
Kind regards,

Yves Vindevogel
Implements