Re: operator exclusion constraints

Out of the ideas in this thread, here are the best and most complete so
far:

Form 1:
WORD1 [ USING index_method ]
( expression WORD2 operator [, ... ] ) index_parameters
[ WHERE ( predicate ) ]

Form 2:
WORD1 [ USING index_method ]
( expression [, ... ] ) WORD2 ( operator [, ...] ) index_parameters
[ WHERE ( predicate ) ]

Word 1:
EXCLUSION
EXCLUDE

Word 2:
CHECK WITH
BY (only works with Form 2)

The current syntax is Form 1 using EXCLUSION/CHECK WITH.

I had trouble making the grammar work using EXCLUDING or EXCLUSIVE.
However, even if we get past that problem, we would want to move the
"USING index_method" clause afterward (otherwise it's too awkward), but
that causes conflicts with the index_parameters (because of the "USING
INDEX TABLESPACE tablespace" clause).

CHECK WITH has a little more meaning than BY, but as Peter says, it
might cause confusion with a regular CHECK constraint. EXCLUDE implies
that the thing on the right hand side is being excluded, when it's
actually specifying what pairs of tuples are mutally exclusive; so I
think EXCLUDE is a little bit too specific.

Right now, I am leaning toward Form 2, and EXCLUSION/BY. So the typical
case would read like:

EXCLUSION USING gist (room, during) BY (=, &&)

Comments, ideas or votes welcome. However, if anyone has any new ideas,
please make an attempt to ensure that the grammar can work and that it's
just as expressive. We've had several productive brainstorming sessions
so far, and I certainly appreciate the input, but I think it's time to
move toward a consensus.

Regards,
Jeff Davis