Michael Graham <mgraham(at)bloxx(dot)com> writes:
> I did suspect that the answer would be that the difficulty out ways the
> benefit. But in terms of driving the planner don't we always want to be
> looking to move all the constants to one side of the expression since
> the planner seems to like those?
Well, you failed to show us any concrete examples of the cases you were
looking at, but no I don't think the planner necessarily likes "all the
constants on one side". Most likely the win cases are where one side of
a WHERE-condition operator exactly matches an index, so you'd need to be
looking for places where rearrangement could make that happen.
regards, tom lane