Stephane Bortzmeyer <bortzmeyer(at)netaktiv(dot)com> writes:
> I have an index on column "numero". When, I use a WHERE numero=8,
> PostgreSQL uses an index scan (OK) but no when using comparison
> operators like numero>8.
That is the default behavior in the absence of any VACUUM ANALYZE
stats (and your explains look suspiciously like default stats).
If you have stats then the choice will depend on how much of the table
the planner estimates will be scanned. An indexscan is generally not
a win for scanning more than a few percent of a table.
regards, tom lane