1251-Average-Selling-Price.tsql

/* Write your T-SQL query statement below */
select p.product_id , 
ROUND(
        ISNULL(
        CAST(
            SUM(
                p.price * u.units 
            )as float
        ) / NULLIF(SUM(u.units),0)
        ,0)
    ,2) as average_price 
from Prices p
left join UnitsSold u
    on p.product_id = u.product_id
    AND u.purchase_date BETWEEN p.start_date AND p.end_date
group by p.product_id