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?
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