Re: ALTER TABLE ... ALTER COLUMN ... SET DISTINCT

On Sun, Apr 5, 2009 at 7:56 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Sat, Apr 4, 2009 at 11:14 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> * Using an integer is bogus.  Use a float4 and forget the weird scaling;
>>> it should have exactly the same interpretation as stadistinct, except
>>> for 0 meaning "unset" instead of "unknown".
>
>> I have a deep-seated aversion to storing important values as float,
>
> [ shrug... ]  Precision is not important for this value: we are not
> anywhere near needing more than six significant digits for our
> statistical estimates.  Range, on the other hand, could be important
> when dealing with really large tables.  So I'm much more concerned
> about whether the definition is too restrictive than about whether
> some uninformed person complains about exactness.

I thought about that, and if you think that's better, I can implement
it that way. Personally, I'm unconvinced. The use case for
specifying a number of distinct values in excess of 2 billion as an
absolute number rather than as a percentage of the table size seems
pretty weak to me. I would rather use integers and have it be clean.
But I would rather have it your way than not have it at all.

...Robert