Help with subtracting values using SQLite & Python

[Extra]

Hello,

I made an inventory system using SQLite and Python. I'm working on a 'checkoutInventory()' function that let's a user add items to a cart and automatically subtracts the items current quantity from the quantity that the user is taking out.

My Question is how do I program a statement that subtracts the user's value from the Quantity column in the SQLite database?

Thanks in advance?

My checkoutInventory() Function right now:

#---------------------------------------------------------------
#                 Checkout Inventory Items 
#---------------------------------------------------------------
def checkoutInventory():

    #Connect to the inventory database (inventory.db)
    connection = sqlite3.connect("inventory.db")
    cursor = connection.cursor()

    print('=============================')
    print('= Checkout From Inventory =')
    print('=============================')
    print("Find an item to checkout by entering it's ID or Name")
    print('(1) Checkout Item by ID')
    print('(2) Checkout Item by Name')
    print('(3) View Cart')
    CHOICE = input("Enter choice: ")

    #----- Update Item by ID -----
    #Choose Item to update by ID
    if CHOICE == '1':
        userQueryID = input('Item ID: ')

        #->Show info for the currently selected item
        cursor.execute('SELECT * FROM items WHERE ID = ?', (userQueryID,))
        result = cursor.fetchall()
        #Print Results/Info in rows
        print('\n--------------------')
        print('Current Info For Item: ' + userQueryID)
        print('--------------------')
        for row in result:
            print('\n--------------------')
            print("Item ID: ", row[0])
            print("Item Name: ", row[1])
            print("Item Quantity: ", row[2])
            print("Item Price: $", row[3])
            print("Item Sell Price: $", row[4])
            print("Item Description: ", row[5])
            print("Item Category: ", row[6])
            print("Item Location: ", row[7])
            print("Last Updated: ", row[10])
            print('--------------------\n')

        #-->Bring up checkout menu
        print('------------------------------')
        print("Would you like to add this item to cart?")
        print('(y) Yes')
        print('(n) No')
        CHOICE = input("Enter choice: ")

        #Yes
        if CHOICE == 'y' or CHOICE == 'Y':
            #Ask for quantity
            userQueryQuantity = int(input('How much quantity are you taking: '))
            #Remove the quantity from the inventory
            #TODO: Update this Update statement so it subtracts user's value from current quantity:
            cursor.execute("UPDATE items SET Quantity = ? WHERE ID = ?" , (userQueryQuantity, userQueryID,))
            connection.commit()
            #Add item to cart
            #TODO: Make somthing that stores the currently selected item (maybe a list?)
            #That way the user can add more stuff to the cart or actually checkout(which will clear the cart
            # since the quantity values have alreday beeen subtracted)
            print('The item with the ID: ' + userQueryID + 'has been added to cart')

        #No
        elif CHOICE == 'n' or CHOICE == 'N':
            #Return to Checkout Menu
            checkoutInventory()