Is the COMMUTATOR clause required for self commutative operators?

[btober]

In the command

CREATE OPERATOR name (
PROCEDURE = func_name
[, LEFTARG = lefttype ] [, RIGHTARG = righttype ]
[, COMMUTATOR = com_op ] [, NEGATOR = neg_op ]
[, RESTRICT = res_proc ] [, JOIN = join_proc ]
[, HASHES ] [, MERGES ]
[, SORT1 = left_sort_op ] [, SORT2 = right_sort_op ]
[, LTCMP = less_than_op ] [, GTCMP = greater_than_op ]
)
Is omitting the COMMUTATOR option a problem at all in case of
self-commutative operators? That is, if I define

CREATE OPERATOR public.+(
PROCEDURE = numeric_add_null,
LEFTARG = numeric,
RIGHTARG = numeric,
COMMUTATOR = +)
(where numeric_add_null is a function that handles in NULLs in a
non-standard, but more useful way), since "+" is self commutative, is it
necessary to include it here? Any advantage or disadvantage to ommitting
or including it?

~Berend Tober


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[Peter Eisentraut]

bt****@seaworthysys.com wrote:

In the command

CREATE OPERATOR name (
PROCEDURE = func_name
[, LEFTARG = lefttype ] [, RIGHTARG = righttype ]
[, COMMUTATOR = com_op ] [, NEGATOR = neg_op ]
[, RESTRICT = res_proc ] [, JOIN = join_proc ]
[, HASHES ] [, MERGES ]
[, SORT1 = left_sort_op ] [, SORT2 = right_sort_op ]
[, LTCMP = less_than_op ] [, GTCMP = greater_than_op ]
)
Is omitting the COMMUTATOR option a problem at all in case of
self-commutative operators?

It's an optimization clause, so if you omit it then you prevent certain
optimizations. See
http://www.postgresql.org/docs/curre....html#AEN29826
for details.
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[Tom Lane]

<bt****@seaworthysys.com> writes:

Is omitting the COMMUTATOR option a problem at all in case of
self-commutative operators?

At the moment it only really matters for operators that are used in
top-level WHERE clauses --- which lets out anything that doesn't return
boolean. But I'd say that as a matter of style, if the operator is
self-commutative you should mark it so. Some day the system might
pay attention.

regards, tom lane

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