INSERT INTO TMP_TXN ......
SELECT .......
  FROM TXN (160m rows), CUSTOMERS (1m rows), PRODUCTS (1k rows)
 WHERE TXN.TXN_DATE = p_date
   AND TXN.TXN_AMOUNT > 0
   AND TXN.PRODUCT_ID = PRODUCTS.PRODUCT_ID
   AND PRODUCTS.PRODTYPE_ID IN ('1', '12', '13');
   AND TXN.CUSTOMER_ID = CUSTOMERS.CUSTOMER_ID
   AND CUSTOMERS.CUSTOMER_STATUS LIKE 'A%'

FOR item IN (SELECT .....
              FROM TXN (160m rows), CUSTOMERS (1m rows), PRODUCTS (1k rows)
              WHERE TXN.CUSTOMER_ID = CUSTOMERS.CUSTOMER_ID
                AND CUSTOMERS.CUSTOMER_STATUS LIKE 'A%'
                AND TXN.PRODUCT_ID = PRODUCTS.PRODUCT_ID
                AND PRODUCTS.PRODTYPE_ID IN ('1', '12', '13')
                AND TXN.TXN_DATE = p_date
                AND TXN.TXN_AMOUNT > 0
              ORDER BY CUSTOMER_ID);
  LOOP
     IF item.customer_id <> customer_id_old THEN
     etc.