ora-00937

Hi,

Please tell me the correct syntax to be modified for below error:-- 

select to_char(end_interval_time, 'MM/DD/YYYY') "Date",
       sum(a.time_waited_micro)/sum(a.total_waits)/10000 c1,
  2    3         sum(b.time_waited_micro)/sum(b.total_waits)/10000 c2,
  4         (sum(a.total_waits) / sum(a.total_waits + b.total_waits)) * 100 c3,
  5         (sum(b.total_waits) / sum(a.total_waits + b.total_waits)) * 100 c4,
  6         (sum(b.time_waited_micro)/sum(b.total_waits)) /
  7  (sum(a.time_waited_micro)/sum(a.total_waits)) * 100 c5
  8  from dba_hist_system_event a, dba_hist_system_event b, dba_hist_snapshot c