Andrew - Supernews <[EMAIL PROTECTED]> writes: > On 2006-12-13, Tom Lane <[EMAIL PROTECTED]> wrote: >> BTW, I think it's possible to prove that there need never be two for the >> case of both sides the same datatype.

> Counterexample even for a single data type: define an operator x =* y > which is true when 2x = y. This is mergejoinable using the following > operators: SORT1 = <, SORT2 = <, LTCMP = (2x < y), RTCMP = (2x > y) > (which is of course the same sortops as for regular =). I think not --- the corresponding sort operators would have to be "2x < y" etc, else the trichotomy law fails, and so do all standard sort algorithms. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate