What happens if we insert a key object in a Hash Map which is already existing ??

Question

I'm using Informatica Power Center 9.1.0 and have blocked with below usecase.

For any given key, delete existing records from target table and insert the records from soruce to same target table and both delete and insert should happen in a single transaction.

Source data:

BusDate   Order Product Quantity
21-May    O1    Phone        100
21-May    O1    Tab           50
21-May    O1    Cam           75
21-May    O1    PC           200
21-May    O2    Phone        150 
21-May    O2    PC            50

Source data is as mentioned in above tabular fomrat, when we are writing to target, delete existing data for given business date and order id combination and insert new data in same transaction.

In above example for Order 1 (O1) and BusDate 5/21 we want to delete all existing records in target table and insert all 4 records in same transaction.

Here how it looks if I need to do same in SQL:

BEGIN TRANSACTION

DELETE target_table
WHERE BusDate = '5/21/2014'
AND Order = 'O1'

INSERT target_table
SELECT *
FROM input_table
WHERE BusDate = '5/21/2014'
AND Order = 'O1'

COMMIT TRANSACTION