Creating an SQL query that eliminates duplicate months/year - sql

Question

Hello Stack Overflow community - hopefully i'm on the right track with this one, but i'm trying to write a query where a report out shows the number of orders placed by month/year. The report currently brings up all the days where i'm trying to join them all by month/year collectively. Hopefully this makes sense, i'm pretty new to this, be gentle please ;)
select distinct month(o.orderdate) 'Month',
year(o.orderdate) 'Year', sum(od.Quantity) as Orders
from OrderDetails od
join Products p
on od.ProductID = p.ProductID
join Orders o
on od.OrderID = o.OrderID
group by o.orderdate
Order by year, month asc;

Answer 1

You need to group by what you want to define each row. In your case, that is the year and month:
select year(orderdate) as yyyy, month(o.orderdate) as mm,
sum(od.Quantity) as Orders
from OrderDetails od join
Products p
on od.ProductID = p.ProductID join
Orders o
on od.OrderID = o.OrderID
group by year(o.orderdate), month(o.orderdate)
Order by yyyy, mm asc;
Notes:
I changed the column names to yyyy and mm so they do not conflict with the reserved words year and month.
Don't use single quotes for column aliases. This is a bad habit that will eventually cause problems in your query.
I always use as for column aliases (to help prevent missing comma mistakes), but never for table aliases.
The product table is not needed for this query.
Edit: If you want a count of orders, which your query suggests, then this might be more appropriate:
select year(o.orderdate) as yyyy, month(o.o.orderdate) as mm,
count(*) as Orders
from orders o
group by year(o.orderdate), month(o.orderdate)
Order by yyyy, mm asc;

Answer 2

You have to group by month and year
select distinct month(o.orderdate) 'Month',
year(o.orderdate) 'Year', sum(od.Quantity) as Orders
from OrderDetails od
join Products p
on od.ProductID = p.ProductID
join Orders o
on od.OrderID = o.OrderID
group by month(o.orderdate), year(o.orderdate)
Order by [Year],[month]