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

On Sun, May 3, 2009 at 3:13 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Mon, Apr 6, 2009 at 11:15 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> So based on this comment and Stephen's remarks, I'm going to assume
>> that I'm succumbing to a fit of unjustified paranoia and re-implement
>> as you suggest.
>
> OK, new version of patch, this time with the weird scaling removed and
> the datatype changed to float4.
>

In this paragraph i think you mean: "ALTER TABLE ... ALTER COLUMN ...
SET DISTINCT"?
   <para>
+    The analyzer also estimates the number of distinct values that appear
+    in each column.  Because only a subset of pages are scanned, this method
+    can sometimes be quite inaccurate, especially for large tables.  If this
+    inaccuracy leads to bad query plans, the analyzer can be forced to use
+    a more correct value with <command>ALTER TABLE ... ALTER COLUMN ... SET
+    STATISTICS</command> (see <xref linkend="sql-altertable"
+    endterm="sql-altertable-title">).
+   </para>

--
Atentamente,
Jaime Casanova
Soporte y capacitación de PostgreSQL
Asesoría y desarrollo de sistemas
Guayaquil - Ecuador
Cel. +59387171157