Re: Why is n_distinct always -1 for range types?

On Thu, Sep 19, 2013 at 1:47 PM, Josh Berkus <josh@agliodbs.com> wrote:
> 4. n-distinct will still be listed as -1 (unique) for the column.
>
> Why?


Because of this:

https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/rangetypes_typanalyze.c#L205

We only collect and use histograms of lower and upper bounds for range
types, and the fraction of empty ranges.

--
Regards,
Peter Geoghegan