I am trying to update one table using a subquery that totals several transactions from another table. I cannot figure how to link specific rows from my parent table to the rows in my subquery. I keep getting the ORA-01427: Subquery returns more than one row. I was hoping to update several records at a time by joining the update table to the subquery. When I break down each section into select statements, I get the expected results. Below is the script I am using.

update trans a
set activityfeeamt =
    (select sum(transled.totaldolamt * -1)Fee
      from transled,
         (select planid, transid, activityfeeamt from trans where planid = '0003') t
      where transled.planid = t.planid and transled.transid = t.transid 
      and a.transid = t.transid and a.transid = transled.transid
      and transled.transtypecd = 'Di'
      and transled.planid = '0003' 
      group by transled.transid, transled.planid, transled.ssnum, t.activityfeeamt
      having sum(transled.totaldolamt * -1) < t.activityfeeamt)
where a.planid = '0003' 
and a.transid in 
      (select transid
      from trans 
      where planid = '0003' and transid in
      (select transid from transled where planid = '0003' 
      and transtypecd = 'Di' and transid in (176, 179))

update t1 
set  col = (
  select ...
  from   t2
  where  t1.xyz = t2.abc -- this join must give one row for each row of t1
);