Question

I need the number of line items per Order.

In this example, order 10 has 0 and order 11 has 2 lines.

IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'dbo.OrderDetail') AND type in (N'U'))
DROP TABLE OrderDetail
IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'dbo.OrderHeader') AND type in (N'U'))
DROP Table OrderHeader
GO
CREATE TABLE OrderHeader(
OrderHeaderID Int Primary Key Identity(10,1),
CustID Int)
GO
CREATE TABLE OrderDetail(
OrderDetailID Int Primary Key Identity(100,1),
OrderHeaderID Int REFERENCES OrderHeader,
ItemID Int)
GO
DECLARE @OrderHeaderID Int
INSERT INTO OrderHeader(CustID) VALUES(1000)
INSERT INTO OrderHeader(CustID) VALUES(1001)
SET @OrderHeaderID=SCOPE_IDENTITY()
INSERT INTO OrderDetail(OrderHeaderID,ItemID) VALUES(@OrderHeaderID,3)
INSERT INTO OrderDetail(OrderHeaderID,ItemID) VALUES(@OrderHeaderID,4)
GO
SELECT 
OrderDetailID,ItemID,OrderHeader.OrderHeaderID,CustID
FROM OrderDetail
JOIN OrderHeader
ON OrderDetail.OrderHeaderID=OrderHeader.OrderHeaderID
-- 

This is where I need help
I need COUNT(*)

FROM OrderDetail WHERE OrderDetail.OrderHeaderID=OrderHeader.OrderHeaderID
SELECT OrderHeader.OrderHeaderID,CustID,CountOfOrderDetail
FROM OrderHeader
JOIN OrderDetail
ON OrderDetail.OrderHeaderID=OrderHeader.OrderHeaderID

Answer 1

select 
   ord.OrderHeaderID
   , count(det.ItemID)
from
   OrderHeader ord
left outer join
   OrderDetail det
on
   det.OrderHeaderID = ord.OrderHeaderID
group by
   ord.OrderHeaderID