Calculating using SUM, query does not work? - mysql

Question

I have two tables.
a) ai_account
b) ai_order_product
i want to do some calculations for particular supplier_id.
1, totalAmount, i want to do something like
SUM(ai_order_product.quantity * ai_order_product.cost)
2, amountPaid, this is total amount paid by the supplier that will be
something like SUM(ai_account.amount) with reference to supplier_id.
3) balance, this will be calculated by SUM(ai_order_product.quantity *
ai_order_product.cost) - SUM(ai_invoice.amount)
4) lastPayment date, that will be MAX(ai_account.addDate).
i tried doing something like this.
SELECT SUM(op.quantity * op.cost) as totalAmount,
SUM(ac.amount) as amountPaid,
SUM(op.quantity * op.cost) - SUM(ac.amount) as balance,
MAX(ac.addDate) as lastPayment
FROM ai_order_product op
LEFT JOIN ai_account ac
ON (op.supplier_id = ac.trader_id)
WHERE op.supplier_id = 42
it does not work properly, it fetches some unexpected values, whereas the result for the above being expected is,
for supplier_id = 42,
1) totalAmount = 1375,
2) amountPaid = 7000,
3) balance = -5625,
4) lastPayment = 2011-11-23
and for supplier_id = 35,
1) totalAmount = 1500,
2) amountPaid = 43221,
3) balance = -41721,
4) lastPayment = 2011-11-28
and for supplier_id = 41
1) totalAmount = 0
2) amountPaid = 3000,
3) balance = -3000,
4) lastPayment = 2011-11-09
i want to fetch one row by supplier_id.
P.S: i just entered some dummy values that is why the calculations are mostly negative whereas in application the calculated values will be positive.

Answer 1

Thats because each "ai_order_product" row is getting counted multiple times (once for each row present in the ai_account table).
Try this:
SELECT
op.totalAmount as totalAmount
, SUM(ac.amount) as amountPaid
, op.totalAmount - SUM(ac.amount) as balance
, MAX(ac.addDate) as lastPayment
FROM (
select supplier_id, sum(quantity * cost) as totalAmount
from ai_order_product
group by supplier_id) op
LEFT JOIN ai_account ac ON (op.supplier_id = ac.trader_id)
WHERE op.supplier_id = 42
This may be slightly off, but this general logic should work.

Answer 2

You have to use to state GROUP BY, when using aggregate functions like SUM in SELECT statements.
SELECT op.supplier_id as supplierId,
SUM(op.quantity * op.cost) as totalAmount,
SUM(ac.amount) as amountPaid,
SUM(op.quantity * op.cost) - SUM(ac.amount) as balance,
MAX(ac.addDate) as lastPayment
FROM ai_order_product op
LEFT JOIN ai_account ac
ON (op.supplier_id = ac.trader_id)
GROUP BY op.supplier_id
HAVING supplierId = 42

Answer 3

SELECT
SUM(op.quantity * op.cost) as totalAmount
, ac2.amountPaid
, SUM(op.quantity * op.cost) - ac2.balance
, ac2.lastPayment
FROM ai_order_product op
LEFT JOIN (SELECT
ac.supplier_id
, MAX(ac.addDate) as lastPayment
, SUM(ac.amount) as balance
FROM ai_account ac
WHERE (op.supplier_id = ac.supplier_id)
GROUP BY ac.supplier_id) ac2 ON (ac2.supplier_id = op.supplier_id)
WHERE op.supplier_id = 42
GROUP BY op.supplier_id
The group by clauses kick in when you're selecting more than one supplier_id.

Answer 4

Notice that your expected and actual values are doubled. After entering your sample data and running the query, I get (for supplier_id = 42)
+-------------+------------+---------+-------------+
| totalAmount | amountPaid | balance | lastPayment |
+-------------+------------+---------+-------------+
| 2750 | 14000 | -11250 | 2011-11-23 |
+-------------+------------+---------+-------------+
That's because you've got 2 rows in each table that match the join criteria, causing a doubling of the results.

Answer 5

I think you need to first get the sub totals for one of the tables so that you only have 1 row coming back. thus the inner select here returns the max and the sum, so when you join to it you only get 1 row.
SELECT SUM(op.quantity * op.cost) as totalAmount,
ac.addDate as lastPayment,
ac.amount as amountPaid,
SUM(op.quantity * op.cost) - SUM(ac.amount) as balance
FROM ai_order_product op
INNER JOIN (
SELECT max(IaiaddDate) as addDate, sum(iai.amount) as Amount, iai.supplier_ID
FROM ai_account iai
Group by supplier_ID) ac
ON AC.Supplier_ID = Op.Supplier_ID
WHERE op.supplier_id = 42
Group by Ac.addDate, ac.amount, op.supplier_ID --Just incase where clause is left off.