SQL SELECT and SUM from three - sql

Question

I have been cracking my head for hours on what I thought to be simple SQL SELECT command. I searched every where and read all questions related to mine. I tried an SQL Command Builder, and even read and applied complete series of SQL tutorials and manuals to try to build it from scratch understanding it (which is very important for me, regarding next commands I'll eventually have to build...).
But now I'm just stuck with the results I want, but on separates SELECT commands which I seem to be unable to get together !
Here is my case : 3 tables, first linked to the second with a common id, second linked to the third with another common id, but no common id from the first to the third. Let's say :
Table A : id, name
Table B : id, idA, amount
Table C : id, idB, amount
Several names in Table A. Several amounts in Table B. Several amounts in Table C. Result wanted : each A.id and A.name, with the corresponding SUM of B.amount, and with the corresponding SUM of C.amount. Let's say :
A.id
A.name
SUM(B.amount) WHERE B.idA = A.id
SUM(C.amount) WHERE C.idB = B.id for each B which B.idA = A.id
It's okay for "the first three columns", and "the first two columns and the fourth", both with a WHERE clause and/or a LEFT JOIN. But I can't achieve cumulating all fourth columns together without messing everything !
One could say "it's easy, just put an idA column in Table C" ! Should be easier, sure. But is it really necessary ? I don't think so, but I could be wrong ! So, I just please anyone (who I will give an eternal "SQL God" decoration) with SQL skills to answer laughing "That's so simple ! Just do that and you are gone ! Stupid little newbies..." ;)
Running VB 2010 and MS SQL Server
Thanks for reading !

Answer 1

Try this:
SELECT A.Id, A.Name, ISNULL(SUM(B.amount), 0) as bSum, ISNULL(SUM(C2.Amount), 0) as cSum
FROM A
LEFT OUTER JOIN B ON A.Id = B.idA
LEFT OUTER JOIN (SELECT C.idB, SUM(C.AMOUNT) AS Amount FROM C GROUP BY C.idB) AS C2 ON C2.idB = B.Id
GROUP BY A.Id, A.Name

Answer 2

Try this:
SELECT
a.id,
a.name,
sum(x.amount) as amountb,
sum(x.amountc) as amountc
from a
left join (
select
b.id,
b.ida,
b.amount,
SUM(c.amount) as amountc
from b
left join c
on b.id = c.idb
group by
b.id,
b.amount,
b.ida
) x
on a.id = x.ida
group by
a.id,
a.name
This should give you the result set you're looking for. It sums all C.Amount's for each B.id, then adds it all together into a single result set. I tested it with a bit of sample data in MSSQL, and it works as expected.

Answer 3

Select a.id, a.name, sum(b.amount), sum(c.amount)
from a inner join b on a.id = b.idA
inner join c on b.id = c.idB
group by a.id, a.name

Answer 4

You need to add them separately:
select a.id, a.name, (coalesce(b.amount, 0.0) + coalesce(c.amount, 0.0))
from a left outer join
(select b.ida, sum(amount) as amount
from b
group by b.ida
) b
on a.id = b.ida left outer join
(select b.ida, sum(amount) as amount
from c join
b
on c.idb = b.id
group by b.ida
) c
on a.id = c.ida
The outer joins are to take into account when b and c records don't both exist for a given id.