On Wed, Mar 31, 2010 at 1:07 PM, Kevin Grittner
<Kevin.Grittner@wicourts.gov> wrote:
> Robert Haas <robertmhaas@gmail.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