"Andrus" <kobruleht2@xxxxxx> writes: > I have lot of autogenerated from projection queries in form > SELECT source.c1, source.c2, t1.col1, t1.col2, ... > FROM (SELECT c1, c2, c3, ..... , c20 FROM ... WHERE ... ) source > LEFT JOIN t2 USING (somecolumn) > Main SELECT uses only few columns (source.c1 and source.c2 in this sample) > from source projection. > 1. Does selecting of unused columns ( c3 ... c20) affect to query prefomance Don't worry about it. All modern Postgres versions ignore columns that aren't actually used in the query --- at least for examples as simple as this one. In cases where you intentionally defeat optimization (eg via OFFSET 0 in a sub-select) it's possible that the sub-select will compute all its output columns even though the upper query doesn't use 'em all. The width field in EXPLAIN output offers a good hint as to how many columns the query is actually fetching. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
