Hello Pavel,
I try to create operator + for varchar and integer with Oracle behave.
create or replace function sum(varchar, int)
returns int as $$ select $1::int + $2 $$ language sql;
create operator + (function = sum, leftarg = varchar, rightarg = int,
commutator = +);
create table foo2(a varchar);
insert into foo2 values('10');
select a + 1 from foo2; -- it is ok
but
select 1 + a from foo2; -- fails
ERROR: operator is only a shell: integer + character varying
LINE 1: select 1 + a from foo2;
Why? This should be solved by COMMUTATOR = +
Nope. I understand commutator to be an optimization thing declaration for
joins, it does not create another operator per se.
See
https://www.postgresql.org/docs/current/static/xoper-optimization.html#id-1.8.3.17.4
Se in particular the end paragraph: you have created a "dummy" because
there is no existing int+varchar operator.
Probably you want to declare another (varchar, int) function and another
operator for varchar + int, which has the initial one as a commutator.
I'm wondering whether you could use varchar to int implicit cast instead.
--
Fabien.
