select p.ProductId
    ,sum(od.Quantity) as TotalQuantity
from Products p
join [Order Details] od
    on p.ProductId=od.Productid
group by p.ProductId

select p.productid
    ,p.ProductName
    , sum(od.quantity) as TotalQuantity
from products p
join [Order details] od
    on p.productid=od.productid
group by p.productid

Msg 8120, Level 16, State 1, Line 1
Column 'products.ProductName' is invalid in the select list because
it is not contained in either an aggregate function or the GROUP BY clause.`

select p.productid, p.ProductName, sum(od.quantity) as TotalQuantity from
products p  join [Order details] od on p.productid=od.productid
group by p.productid, p.ProductName

select p.productid
, min(p.ProductName) as ProductName
, sum(od.quantity) as TotalQuantity
from products p
join [Order details] od
    on p.productid=od.productid
group by p.productid