The following query returns productSum as null:

var productName = "productTwo"
db.query("SELECT sum(?) as productSum FROM orders WHERE email = ? AND productTwoName = ?",
[productName, email, productNamesArray[i]],

But replacing sum(?) with sum(productTwo) & removing productName gives the desired sum result.

How can I query using a variable value instead of manually including the name in the query?