T E Schmitz <mailreg@numerixtechnology.de> writes:
> As far as I can see (via EXPLAIN), both DISTINCT and GROUP BY will lead
> to a sequentail scan. Is that correct?
I'm not sure why you expect something different. The query requires
visiting every row of the table in any case --- else it might miss
values that occur only once --- therefore a seqscan is most efficient.
The planner will consider plans that involve an indexscan, but only
as a substitute for doing an explicit sort before a uniq-style grouping
step. Generally the explicit sort will win that comparison. And a
hash grouping step probably dominates them both.
regards, tom lane
