El 31/10/14 a las 04:46, Jayadevan M escibió: > Hi all, > > I am going through PostgreSQL documentation on how row estimation is > done in PostgreSQL. > http://www.postgresql.org/docs/current/static/row-estimation-examples.html > There is a reference to cardinality (rel_cardinality) there. But that > is an estimate of the number of rows in the table, right? > > How many unique values are there in a column (cardinality), that is > estimated while finding out selectivity? > > Did you look into pg_stats view? There is a column colled n_distinct that indicates that (-1 all distinct, 1 none distintct). That's what you are asking about? -- -- Emanuel Calvo http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
