Обсуждение: pg_stats explained ... ?

Morning all ...
Can someone explain to me how I should read this:
       tablename        |          attname           | avg_width | n_distinct
-------------------------+----------------------------+-----------+------------iwantu_pro_week         | uid
           |         8 |         -1iwantu_pro_week         | pro_week_agent             |         9 |
9iwantu_pro_week        | pro_week_time              |         8 |  -0.976321iwantu_pro_week         | pro_week_post
         |         5 |          2iwantu_pro_week         | pro_week_club              |         2 |          1
 

n_distinct, I'm taking it, of -1 means its a UNIQUE INDEX, and the
positive numbers are exact #'s ... but, -0.976321? :)

Also, how is the avg_width interpreted?

"Marc G. Fournier" <scrappy@hub.org> writes:
> n_distinct, I'm taking it, of -1 means its a UNIQUE INDEX, and the
> positive numbers are exact #'s ... but, -0.976321? :)

"Almost unique", evidently.  See stadistinct at
http://www.ca.postgresql.org/users-lounge/docs/7.2/postgres/catalog-pg-statistic.html

> Also, how is the avg_width interpreted?

Just what you'd expect: average stored width, in bytes, of non-NULL
entries in the column.
        regards, tom lane