I’m afraid the formula you use is not correct.
This: slavetrackers[slavetrackersPoints] is a list of values.
because of it,this expression: slavetrackers[slavetrackersPoints] - gifts[giftsPoints] is a list type, operating a list subtraction.
If you want to get a number, you may prefer using: SUM(slavetrackers[slavetrackersPoints]) - SUM(gifts[giftsPoints])
I don’t see any virtual column on your screenshot, did you cut the snap ?
Furthermore, I don’t see the relation between your two tables on the screenshots ? (this is a virtual column as well)
Also, can you please show your action setting with the “dollar” button ?
I’m sorry, I’m not sure of getting what you want to achieve.
When i click on dollars the field slavetrackersPoints of table slavetrackers set slavetrackers[slavetrackersPoints] = slavetrackers[slavetrackersPoints] - gifts[giftsPoints]
This is in contradiction with the screenshot of your action “Acheter”.
If you choose one “gifts” the slavetrackersPoints is update with the value Point of gifts selected.
This goes to my first question: what is the relation between your two tables ? You must have one column in the slaveTracker Table referring to your Gifts Table. Otherwise, you cannot specify which item you refers in your sum.
I suggest you have a look to this sample app, just click on “Look under the hood” button.
This is a basic app, and the column “Total Stock Available” in the Table Items will reveal the main interest of the virtual column.
Also, the Item ID in the Inventory Table, which refers to the Items table.