pinker wrote >>> rhaas=# explain select a from generate_series(1,100) a union select a >>> from generate_series(1,100) a; >>> QUERY PLAN >>> -------------------------------------------------------------------------------------- >>> HashAggregate (cost=45.00..65.00 rows=2000 width=4) >>> -> Append (cost=0.00..40.00 rows=2000 width=4) > > > Why in this case the estimated number of rows is 2000? Is it standard > planner behavior? http://www.postgresql.org/docs/9.1/static/sql-createfunction.html Note the "ROWS" property. Functions are black-boxes to the planner so it has no means of estimating a row count. So a set returning function uses 1,000 and all others use 1. Determining "COST" is similarly problematic. David J. -- View this message in context: http://postgresql.1045698.n5.nabble.com/UNION-and-bad-performance-tp3301375p5806450.html Sent from the PostgreSQL - performance mailing list archive at Nabble.com.
