hi @Yalcin_Arsan ,
I agree with @Breno_Nunes that it is for multiple reasons better to split the sales and stock table and use buttons with a modifyRow logic.
You can create a set up as suggested by @Piet_Strydom , it is not too difficult
However it is an expensive calculation, each time all rows in the table are evaluated to generate the rowIndex and it will slow down your doc significantly over time when your table grows:
thisTable.Find(thisRow)
About how to modify a row, you can have a look below: 
The buttons keep the doc also fast, you only press them (activate them) when needed, for the rest of the time the code stored in the buttons sleeps and does not consume anything.
Cheers Christiaan