Asp.Net autocomplete

I have to add data in database using autocomplete. if the data exist the old data will overwrite.if the data is not available new recourd will added in database.

eg- i have Product name, Product Qty and Product Price three text box if the product name is exist  it display product price and also user can update price.and product name is not exist user can able to add new recourd. .... plz help..