2013/1/31 Vincent Veyron <vv.lists@xxxxxxxxxx>: > Le jeudi 31 janvier 2013 à 09:49 +0100, Pavel Stehule a écrit : > >> any join where result is related to some function result can be very >> slow, because estimation will be out and any repeated function >> evaluation is just expensive. >> > > Hi Pavel, > > Thank you for the correction. Since we're at it, I have a question > regarding functions in a query : > > Suppose I have a query of the form > > SELECT my_function(column_1), column_2 > FROM my_table > GROUP BY my_function(column_1) > ORDER BY my_function(column_1); > > where my_function is a user defined function. > > How many times is the function computed? if function is stable or immutable, then once per row Pavel > > > > > -- > Salutations, Vincent Veyron > http://marica.fr/site/demonstration > Logiciel de gestion des contentieux juridiques et des sinistres d'assurance > -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
