Re: Implied Functional Index use

Am Dienstag, 11. Juli 2006 23:31 schrieb Tom Lane:
> We could invent some more-complex concept involving "well, this is
> equality, but there are some functions for which f(x) might differ
> from f(y) anyway" and then mark the presumably-few functions that
> could produce divergent results --- examples are sgn() for float8
> and anything dependent on dscale for numeric.  This seems ugly and
> error prone however.

From a mathematical point of view, it seems cleaner to attach this property to
functions, not operators, namely, "this function preserves the following
relations".  This would allow extending Simon's idea to other operators such
as > and < and possibly more mind-boggling cases with geometric operators and
such.

Admittedly, this would put a lot of additional typing load on function
authors, but perhaps it's safer that way.

--
Peter Eisentraut
http://developer.postgresql.org/~petere/