[MonetDB-users] substing made monetdb very very slow

Hi all: we are testing monetdb on a sql select substring(fact_bk,1,1) as aa,sum(1) as recordcount from f_activity group by aa the table f_activity have about 5 million rows. when i run this sql, monetdb need about 30 seconds . (if we use another no calculated column, it need only 1-3 seconds) when I run this sql on sql server, it needs only 7 seconds. is monetdb not good at calculated column? or we have made some mistake? please tell me the reason, thank you. lixiaohua Shanghai,China