want to update records of 2nd table when i insert values in 1st table

[soahil]

hello
I am facing a problem.
i have two tables named "BILL_DETAIL" and "COMPANY"
both structure is as follws:
---------------------
"BILL_DETAIL"
---------------------
BILL_ID NOT NULL NUMBER(38)
S_HEAD_CODE NOT NULL VARCHAR2(12)
SR_NO NOT NULL NUMBER(38)
BILL_AMOUNT NUMBER(38)
DESCRIPTION NOT NULL VARCHAR2(1000)
CATEGORY_CODE NUMBER(38)
COMP_ID NUMBER(38)
TAX_AMOUNT NUMBER(38)
TAX_ID NUMBER(38)
--------------------------------------------------------
"COMPANY"
--------------------------------------------------------
Name Null? Type
------------------------------- -------- ----
COMP_ID NOT NULL NUMBER(38)
COMP_NAME NOT NULL VARCHAR2(40)
CONTACT_PERSON VARCHAR2(25)
COMP_ADDRESS VARCHAR2(200)
NTN VARCHAR2(15)
OWNER_CNIC VARCHAR2(15)
TOTAL_AMOUNT_PURCHASE NUMBER(38)
TOTAL_AMOUNT_REPAIR NUMBER(38)
------------------------------------------------

I want that when i insert values in "BILL_DETAIL" table and save record. then the BILL_AMOUNT should also be updated in the "COMPANY" table's fields "TOTAL_AMOUNT_PURCHASE" or "TOTAL_AMOUNT_REPAIR"
Please tell me which trigger i should use and at what level with what code

I will be very thankful.

Thanks n regards

[pragatiswain]

--ASSUMPTIONS:
--1. IN BILL_DETAIL, S_HEAD_CODE SIGNIFIES, IF IT IS A PURCHASE OR REPAIR.
--2. IN BILL_DETAIL TOTAL AMOUNT = BILL_AMOUNT + TAX_AMOUNT
--THE AVOBE ASSUMPTIONS WERE MADE AS THE INFORMATION PROVIDED WAS INADEQUATE.

CREATE OR REPLACE TRIGGER TRG_INS_BILL_DETAIL
AFTER INSERT
ON BILL_DETAIL
FOR EACH ROW
BEGIN
IF (:NEW.S_HEAD_CODE IN (<SPECIFY S_HEAD_CODE VALUES FOR PURCHASE>)) THEN
UPDATE COMPANY
SET TOTAL_AMOUNT_PURCHASE = TOTAL_AMOUNT_PURCHASE + :NEW.BILL_AMOUNT + :NEW.TAX_AMOUNT
WHERE COMP_ID = :NEW.COMP_ID ;
ELSE
UPDATE COMPANY
SET TOTAL_AMOUNT_REPAIR = TOTAL_AMOUNT_REPAIR + :NEW.BILL_AMOUNT + :NEW.TAX_AMOUNT
WHERE COMP_ID = :NEW.COMP_ID ;
END TRG_INS_BILL_DETAIL;


Hope this helps.