How to sum columns when table is joined? - sql

Question

Trying to sum from a table that is joined to another (resulting in multiple rows per row of the first table) it is counting the amount for each of the rows in second table.
Tables:
create table t_orders (
oid int,
cartlink nvarchar(3),
ordertotal float,
ordertax float
);
create table t_cart (
cartlink nvarchar(3),
productid int
);
insert into t_orders (oid,cartlink,ordertotal,ordertax) values
(1,'abc',10, 2),
(2,'cdf',9, 1),
(3,'zxc',11, 3)
;
insert into t_cart (cartlink,productid) values
('abc', 123),('abc', 321),('abc', 987),
('cdf', 123),('cdf', 321),('cdf', 987),
('zxc', 123),('zxc', 321),('zxc', 987)
;
Using following values for t_orders table is more accurate to the problem. Using distinct only counts order 2 and 3 once because both of their totals are 9.
insert into t_orders (oid,cartlink,ordertotal,ordertax) values
(1,'abc',10, 2),
(2,'cdf',9, 1),
(3,'zxc',9, 3)
;
Query and result:
SELECT
SUM(t_orders.ordertotal) AS SumOfTotal,
SUM(t_orders.ordertax) AS SumOfTax
FROM
t_orders
JOIN t_cart ON t_orders.cartlink = t_cart.cartlink
;
SumOfTotal
SumOfTax
90
18
What I want :
SumOfTotal
SumOfTax
30
6
I have to join t_orders -> t_cart -> t_products -> t_manufacturer because I'm trying to sum from t_orders WHERE t_manufacturer.type = 'some value'.

Answer 1

Try this
SELECT SUM(DISTINCT t_orders.ordertotal) AS SumOfTotal
, SUM(DISTINCT t_orders.ordertax) AS SumOfTax
FROM t_orders
JOIN t_cart ON t_orders.cartlink = t_cart.cartlink

Answer 2

"… I'm trying to sum from t_orders WHERE t_manufacturer.type = 'some value'."
Using sub-query:
SELECT
SUM(t1.Total) AS SumOfTotal,
SUM(t1.Tax) AS SumOfTax
FROM
(
SELECT
MAX(t_orders.ordertotal) AS Total,
MAX(t_orders.ordertax) AS Tax
FROM t_orders
JOIN t_cart ON t_orders.cartlink = t_cart.cartlink
JOIN t_products ON t_cart.productid = t_products.pid
JOIN t_manufacturer ON t_products.manufacturerid = t_manufacturer.mid
WHERE t_manufacturer.type = 'some value'
GROUP BY t_orders.oid
) AS t1
Or:
SELECT
SUM(t1.Total) AS SumOfTotal,
SUM(t1.Tax) AS SumOfTax
FROM
(
SELECT
MAX(t_orders.ordertotal) AS Total,
MAX(t_orders.ordertax) AS Tax
FROM t_orders
JOIN t_cart ON t_orders.cartlink = t_cart.cartlink
JOIN t_products ON t_cart.productid = t_products.pid
WHERE t_products.manufacturerid IN (
SELECT mid FROM t_manufacturer WHERE type = 'some value'
) AS t2
GROUP BY t_orders.oid
) AS t1