Re: How can I manually alter the statistics for a column?

[Douglas Alan <darkwater42@xxxxxxxxx>]

If you want something done right, I guess you have to do it yourself!

Here's the answer to my question.  It works great! Or so it seems to:

delete from pg_statistic s
where exists ( select 1
from pg_class as c, pg_attribute as a
where a.attrelid = c.relfilenode

and s.starelid = c.relfilenode
and s.staattnum = a.attnum
and c.relname = 'maindb_astobject'
and attname = 'survey_id'

);

In the above SQL statement, "maindb_astobject" is the name of the table and "survey_id" is the name of the column.  The statement deletes all the statistics for the specified column in the specified table.

|>ouglas

On Mon, Jun 1, 2009 at 2:20 PM, Douglas Alan <darkwater42@xxxxxxxxx> wrote:

I'd like to manually alter the statistics for a column, as for the column in question the statistics are causing Postgres to do the wrong thing for my purposes. (I.e., a Seq Scan, rather than an Index Scan.)  If someone can tell me how to achieve this, I would quite grateful.

Thanks!
|>ouglas


P.S. Actually, for this particular problem, just deleting the statistics would be fine.  I've tried doing:

alter table maindb_astobject alter column survey_id set statistics 0;

And then analyzing the column, but when "statistics"  for a column are set to 0, Postgres seems to leave the current statistics in place, which is not the right thing for me at all.  I can successfully set "statistics" to 1, but that turns out to be one statistic too many.

I've tried settings the statistics via the table "pg_stats", but that turns out to be a view, and Postgres won't allow to me to alter it.

Perhaps I can achieve the end by altering the "pg_statistic" table instead, but that table is more than a bit opaque to me.

P.P.S The Seq Scan is 2-4 orders of magnitude slower than the Index Scan.