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

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, "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 17:13:47
Message-ID: q2h603c8f071003311013x89bf2be8kfcc74e227198a702@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Mar 31, 2010 at 1:07 PM, Kevin Grittner
<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> 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.

Oh, I see.  I thought it was referring to all pairs of rows, but I see
now it's referring to pairs of columns, so it's correct.

...Robert

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