I agree that using a precomputed value in a where clause is a good idea. But it's very likely that computing that value inside a DB engine and fetching a single

I agree that using a precomputed value in a where clause is a good idea. But it's very likely that computing that value inside a DB engine and fetching a single value is going to be faster than fetching 50 values and calculating the product in your app. Also, consider the following case: UPDATE huge_table SET someval = (SELECT PRODUCT(x) ...). Splitting this into 50 million queries wouldn't be a very good solution.