high read tables

Hi list, how can I know highly read / write tables ? I have this stats for dbspaces but following querry returns wrong results as compared to onstat -g iof output. select tabname[1,18], sum(pf_dskreads)::decimal(8,0) diskreads, sum(pf_bfcread)::decimal(8,0) cache_reads, sum(pf_dskwrites)::decimal(8,0) diskwrites, sum(pf_bfcwrite)::decimal(8,0) cache_writes from sysptntab,systabnames where sysptntab.partnum=systabnames.partnum and tabname not matches "sys*" and dbsname not in ("sysmaster","rootdbs","sysutils") and tabname != "TBLSpace" group by 1 order by 1 Thanks for your help