Count quantity for the same id product in a table

Question

I've problem with java (I'm using netbeans) when build an simple application to log product in a table. Product id is entered in a field text and detect it in a database for taking product detail. for default entry, quantity is 1 then if the same product is entered, quantity column adds 1 automatically. It works in first entry. But, when i add other product, it messed up.
how do i fix it?
this the code
https://code.sololearn.com/cR0pGqt1ULal/?ref=app
this the pict
https://i.stack.imgur.com/pV3Gh.png

Answer 1

use the concept of primary and unique key.
while create the table in database..
so that it not mixed up..
while adding information into it..

Answer 2

Thanks for answering