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.
-Kevin