I wrote:
> Yeah, I didn't have any doubt that it was real. Still don't know
> why my test case isn't doing what I expected, though.
Doh: the planner knows that transaction_timestamp() is stable, so
it concludes that the DISTINCT condition is vacuous. There is a
"Unique" node in the plan, but it has zero columns to compare, so
it thinks the tuple are all equivalent and emits only the first.
I had noticed that there was no "Sort" node, but failed to realize
that that implied the "Unique" node was degenerate.
Maybe this is over-optimization, but I think we'd be very sad if
the planner didn't do it; getting rid of useless sort columns is
critical in a lot of situations.
regards, tom lane
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