Re: [SPAM]Re: Questions about 9.0 release note

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Robert Haas" <robertmhaas(at)gmail(dot)com>, "Takahiro Itagaki" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
Cc: "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [SPAM]Re: Questions about 9.0 release note
Date: 2010-03-31 17:07:17
Message-ID: 4BB33AF50200002500030290@gw.wicourts.gov
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Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> This says:
>
> Exclusion constraints ensure that that if any two rows are
> compared on the specified column(s) or expression(s) using the
> specified operator(s), not all of these comparisons will return
> <literal>TRUE</>.
>
> I think that's backwards - the last clause should say "none of
> those comparisons will return <literal>TRUE</>".
>
> Unless I'm confused.

"not all" seems correct. For example, you could be checking the
room number for equality and a range of time for overlap -- both
must be TRUE to have a problem; otherwise you could only schedule
one thing in the room for all time and one thing at a given time
across all rooms.

-Kevin

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