| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: WIP: generalized index constraints |
| Date: | 2009-07-07 18:52:41 |
| Message-ID: | 1246992761.26589.218.camel@monkey-cat.sm.truviso.com |
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| Lists: | pgsql-hackers |
On Tue, 2009-07-07 at 18:36 +0100, Simon Riggs wrote:
> On Tue, 2009-07-07 at 13:22 -0400, Tom Lane wrote:
> It is likely to be useful in the future to allow an index with N
> columns, yet which can provide uniqueness with < N of those columns.
> This capability is known as covered indexes and will be important if
> Heikki writes his index-only scan code.
My patch offers this capability, and the language I suggested would
support it.
In the current version of the patch, just use InvalidStrategy (0)
instead of, say, BTEqualStrategyNumber (3) for the attributes that you
don't want to be a part of the constraint. Some of the proper error
checking is not done yet, but it will work.
Regards,
Jeff Davis
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