Re: Proposed new create command, CREATE OPERATOR CLASS - Mailing list pgsql-hackers

Bill, is there a patch that is ready for application?

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Bill Studenmund wrote:
> On Mon, 29 Oct 2001, Oleg Bartunov wrote:
> 
> > On Thu, 25 Oct 2001, Teodor Sigaev wrote:
> >
> > > >>Wait a second, how can you do that? Doesn't that violate
> > > >>pg_amop_opc_strategy_index ?
> > > >
> > > > This is evidently a bug in the script.  Oleg?
> > >
> > > Make me right if I mistake.
> 
> Don't add @@ to pg_amop.
> 
> > > When we was developing operator @@, I saw that postgres don't use index in
> > > select if operation has not commutator. But operator with different types in
> > > argument can't be commutator with itself. So I maked operator ~~ only for
> > > postgres can use index access for operator @@. There is no any difficulties to
> > > adding index support for operator ~~. The same things is with contrib/tsearch
> > > module.
> > >
> > > But I think that there is not any other necessity in presence ~~.
> 
> ?? An operator with different times in the arguements most certainly can
> be a commutator with itself.
> 
> Try:
> 
> select oid, oprname as "n", oprkind as "k", oprleft, oprright, oprresult,
> oprcom, oprcode from pg_operator where oprleft <> oprright and oprname =
> '+';
> 
> and look at the results. There are a number of pairs of same-name
> commutators: 552 & 553 add int2 to int4, 688 & 692 add int4 to int8, and
> so on.
> 
> Also, I was able to do this:
> 
> testing=# CREATE OPERATOR @@ (
> testing(#    LEFTARG = _int4, RIGHTARG = query_int, PROCEDURE = boolop,
> testing(# COMMUTATOR = '@@', RESTRICT = contsel, join = contjoinsel );
> CREATE
> testing=#  CREATE OPERATOR @@ (
> testing(# LEFTARG = query_int, RIGHTARG = _int4, PROCEDURE = rboolop,
> testing(# COMMUTATOR = '@@', RESTRICT = contsel, join = contjoinsel );
> CREATE
> testing=#
> 
> > Tom,
> >
> > this is interesting question - do we really need commutator to get
> > postgres to use index. This is the only reason we created  ~~ operator.
> 
> Please note: my concern is not with the ~~ operator, it's with trying to
> insert that operator into pg_amop. Well, with trying to insert both the @@
> and ~~ operators in as strategy (amopstrategy) 20. amopclaid and
> amopstrategy are part of a unique index for pg_amop. So you *can't* add
> two operators in the same opclass as the same sequence number.
> 
> Although, given the above example, I think the ~~ operator should be
> renamed the @@ operator. :-)
> 
> I think you do need to have both variants of the operator around. A
> binary, type asymmetric operator without a commutator is less useful. And
> makes lese sense.
> 
> Take care,
> 
> Bill
> 
> 
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