SQL & PL/SQL :: Logic For Update And Delete?

i have three tables: ot_req, ot_po_breakup, and ot_po. when a row is inserted into the ot_po table reffering to ot_req,there is a trigger which creates a seperate reocrd in ot_po_breakup with the details of ot_req ot_req.ri_sys_id as pb_ri_sys_id and ot_req.ri_qty as pb_ri_qty ,pi_sys_id as pb_pi_sys_id .upto this part is okand when i insert also the logic is okay.

i have created a trigger to update the rows in the ot_po_breakup table after insert on ot_poin order of pb_ri_sys_id and pb_pi_sys_id and try to update the values in the columns pb_ves1q, pb_ves2q, and pb_ves3q order. i am trying to take the quantities in ot_po.pi_qty and insert them into the pb_ves1q, pb_ves2q, and pb_ves3q columns of ot_po_breakup where those columns are empty (0 or null) such that the sum of those three columns for that row does not exceed the pb_ri_qty in that row.

My problem is i need to mofify my trigger to do the update and delete , that is whenever the user is updating the column ofot_po.pi_qtythe qty should in ot_po_breakup should get updated accordingly and sum of pb_ves1q,pb_Ves2q and pb_ves3q should be equal to pb_ri_qty and do the same for delete as well

CREATE TABLE OT_REQ
(
RI_ITEM VARCHAR2(20 BYTE),
RI_SYS_ID NUMBER,
RI_QTY NUMBER

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