Performance Tuning :: How To Control Concurrent Inserts Of Record By Parallel Sessions

There is a detail table

There is a summary table

During batch process record is entered in detail table as well as summary table.

The process first checks if record exists in summary table for same group_no and if 'yes' then "updates" the record with the newly added amount (sums it) else inserts a new record
Whereas in the detail table it inserts the record directly

detail table :
group_no doc_no amount
101 doc1 100
101 doc2 200
102 doc3 300
102 doc4 400

summary table :
group_no amount
101 300
102 700

Now if the batch process runs in parallel, (out of many) two different sessions insert same group_no; This is because while sesond session inserts a record, first session inserting the same record (group_no) has not yet committed ; So second session Not knowing that already there is same Group_no (101) inserted, again inserts another record with same group_no rather than summing it.

Can it be solved without using temp table, select for update?