gistfile1.txt

ishida=# create function any_eq (anyelement, anyelement) returns boolean language sql as 'select $1 = $2';
CREATE FUNCTION
ishida=# create operator == (procedure = any_eq, leftarg=anyelement, rightarg=anyelement);
CREATE OPERATOR

ishida=# select 1+2 == 3;
 ?column?
----------
 t
(1 row)

ishida=# select 'abc' == 'abc';
ERROR:  could not determine polymorphic type because input has type "unknown"
ishida=# select 'abc' == 'abc'::text;
 ?column?
----------
 t
(1 row)