Grzegorz Jaśkiewicz wrote:
Can correlation be negative ?
Yes, if the data in the column are in descending order. For example: postgres=# CREATE TABLE foo(id int4); CREATE TABLE postgres=# INSERT INTO foo SELECT 1000 - generate_series(1, 1000); INSERT 0 1000 postgres=# ANALYZE foo; ANALYZE postgres=# SELECT attname, correlation FROM pg_stats WHERE tablename='foo'; attname | correlation ---------+------------- id | -1 (1 row) -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
