Group by with left outer join, exclude nulls - sql

Question

I have an order table and a trip table that includes payment information. It is a many to many relationship - order can split across many trips and one trip could have payment info for a couple of orders and sometimes an order. There is no "Zero" record in the Trips table - so a left join with that value as the key will return a NULL record. I am using SQL 2012
Order table
+----+----------+--------------+
| order_id | trip_nbr | veh_id |
+----+----------+--------------+
| 1 | 12 | 3 |
| 2 | 22 | 6 |
| 2 | 0 | 8 |
| 4 | 25 | 7 |
| 7 | 0 | 11 |
+----+----------+--------------+
Trips table
+----+------------+--------------+
| trip_nbr | payment | veh_id |
+----+------------+--------------+
| 12 | 20.00 | 3 |
| 22 | 123.00 | 6 |
| 22 | 12.50 | 6 |
| 25 | 133.33 | 7 |
+----+------------+--------------+
Here is my query:
select o.order_id,
t.trip_nbr,
sum(t.payment_amt)
from orders o
left outer join trips t
on o.trip_nbr = t.trip_nbr
group by o.order_id,
t.trip_nbr
Results:
+----+----------+--------------+
| order_id | trip_nbr | sum |
+----+----------+--------------+
| 1 | 12 | 20.00 |
| 2 | 22 | 135.50 |
| 2 | NULL | NULL |
| 4 | 25 | 133.33 |
| 7 | NULL | NULL |
+----+----------+--------------+
The problem is, I get lots of information from the orders table and just the payment info from the Trips table. So I don't want to exclude any order records (which would happen if I add the clause "WHERE t.trip_nbr is NOT NULL") - but I don't want to get 2 records in my grouping - one for t.trip_nbr is NULL and one where it finds a match.
Desired results:
+----+----------+--------------+
| order_id | trip_nbr | sum |
+----+----------+--------------+
| 1 | 12 | 20.00 |
| 2 | 22 | 135.50 |
| 4 | 25 | 133.33 |
| 7 | NULL | NULL |
+----+----------+--------------+
I want the unmatched record order_id = 2 to be "summarized away" - but keep the lone record for order_id = 7. The reason is that this table is later join with another table and the extra NULL records are creating duplicates.

Answer 1

This should work:
WITH orders2 AS
(
SELECT *,
N = SUM(CASE WHEN trip_nbr <> 0 THEN 1 ELSE 0 END) OVER(PARTITION BY order_id)
FROM orders
)
SELECT o.order_id,
t.trip_nbr,
SUM(t.payment_amt)
FROM orders2 o
LEFT OUTER JOIN trips t
ON o.trip_nbr = t.trip_nbr
WHERE N = 0 OR (N > 1 AND o.trp_nbr <> 0)
GROUP BY o.order_id,
t.trip_nbr;

Answer 2

You can use a window function like RANK to identify superfluous NULL- valued records and filter them out in an outer query:
select order_id,
trip_nbr,
total_payment
from (
select o.order_id,
t.trip_nbr,
sum(t.payment) as total_payment,
rank() over (partition by order_id
order by case
when t.trip_nbr IS NULL then 2
else 1
end) as rnk
from orders o
left outer join trips t
on o.trip_nbr = t.trip_nbr
group by o.order_id, t.trip_nbr) as t
where t.rnk = 1

Answer 3

If you convert your nulls to zero, then sum "trip_nbr" and "sum" for a given order_id. Would this not solve your challenge?
create table #Order (Order_Id int , Trip_nbr int , Veh_id int )
Create Table #Trips (trip_nbr int , Payment Numeric(13,2), Veh_id int )
insert into #Order (Order_id, Trip_nbr, Veh_id) values (1,12,3)
insert into #Order (Order_id, Trip_nbr, Veh_id) values (2,22,6)
insert into #Order (Order_id, Trip_nbr, Veh_id) values (2,0 ,8)
insert into #Order (Order_id, Trip_nbr, Veh_id) values (4,25,7)
insert into #Order (Order_id, Trip_nbr, Veh_id) values (7,0,11)
insert into #Trips (trip_nbr, Payment, Veh_id) values (12, 20.00 , 3 )
insert into #Trips (trip_nbr, Payment, Veh_id) values (22, 123.00,6 )
insert into #Trips (trip_nbr, Payment, Veh_id) values (22, 12.50 , 6 )
insert into #Trips (trip_nbr, Payment, Veh_id) values (25, 133.33 , 7 )
select Order_id, trip_nbr = sum(trip_nbr), Payment = sum(payment)
from
(
select o.order_id,
t.trip_nbr,
Payment = sum(t.Payment)
from #order o
left outer join #trips t on t.trip_nbr = o.trip_nbr
-- left outer join #order o on t.trip_nbr = o.trip_nbr
group by o.order_id, t.trip_nbr
) x
group by Order_id
order by Order_id