SQLITE update multiple row from stock where we have a product with multiple record

I want to create a trigger for product table to update qty afte开发者_如何学JAVAr selling product .

I have a table of product like this productTB with name and qty fields :

NAME	QTY
'A'	1
'B'	4
'A'	4

I want to write a query for remove 2 qty for 'A' item.

I want the qty of 'A' item be like this

NAME	QTY
'A'	0
'B'	4
'A'	3

How can do this in SQLite?