nested query & transaction - mysql

Question

Update #1: query gives me syntax error on Left Join line (running the query within the left join independently works perfectly though)
SELECT b1.company_id, ((sum(b1.credit)-sum(b1.debit)) as 'Balance'
FROM MyTable b1
JOIN CustomerInfoTable c on c.id = b1.company_id
#Filter for Clients of particular brand, package and active status
where c.brand_id = 2 and c.status = 2 and c.package_id = 3
LEFT JOIN
(
SELECT b2.company_id, sum(b2.debit) as 'Current_Usage'
FROM MyTable b2
WHERE year(b2.timestamp) = '2012' and month(b2.timestamp) = '06'
GROUP BY b2.company_id
)
b3 on b3.company_id = b1.company_id
group by b1.company_id;
Original Post:
I keep track of debits and credits in the same table. The table has the following schema:
| company_id | timestamp | credit | debit |
| 10 | MAY-25 | 100 | 000 |
| 11 | MAY-25 | 000 | 054 |
| 10 | MAY-28 | 000 | 040 |
| 12 | JUN-01 | 100 | 000 |
| 10 | JUN-25 | 150 | 000 |
| 10 | JUN-25 | 000 | 025 |
As my result, I want to to see:
| Grouped by: company_id | Balance* | Current_Usage (in June) |
| 10 | 185 | 25 |
| 12 | 100 | 0 |
| 11 | -54 | 0 |
Balance: Calculated by (sum(credit) - sum(debits))* - timestamp does not matter
Current_Usage: Calculated by sum(debits) - but only for debits in JUN.
The problem: If I filter by JUN timestamp right away, it does not calculate the balance of all time but only the balance of any transactions in June.
How can I calculate the current usage by month but the balance on all transactions in the table. I have everything working, except that it filters only the JUN results into the current usage calculation in my code:
SELECT b.company_id, ((sum(b.credit)-sum(b.debit))/1024/1024/1024/1024) as 'BW_remaining', sum(b.debit/1024/1024/1024/1024/28*30) as 'Usage_per_month'
FROM mytable b
#How to filter this only for the current_usage calculation?
WHERE month(a.timestamp) = 'JUN' and a.credit = 0
#Group by company in order to sum all entries for balance
group by b.company_id
order by b.balance desc;

Answer 1

what you will need here is a join with sub query which will filter based on month.
SELECT T1.company_id,
((sum(T1.credit)-sum(T1.debit))/1024/1024/1024/1024) as 'BW_remaining',
MAX(T3.DEBIT_PER_MONTH)
FROM MYTABLE T1
LEFT JOIN
(
SELECT T2.company_id, SUM(T2.debit) T3.DEBIT_PER_MONTH
FROM MYTABLE T2
WHERE month(T2.timestamp) = 'JUN'
GROUP BY T2.company_id
)
T3 ON T1.company_id-T3.company_id
GROUP BY T1.company_id
I havn't tested the query. The point here i am trying to make is how you can join your existing query to get usage per month.

Answer 2

alright, thanks to #Kshitij I got it working. In case somebody else is running into the same issue, this is how I solved it:
SELECT b1.company_id, ((sum(b1.credit)-sum(b1.debit)) as 'Balance',
(
SELECT sum(b2.debit)
FROM MYTABLE b2
WHERE b2.company_id = b1.company_id and year(b2.timestamp) = '2012' and month(b2.timestamp) = '06'
GROUP BY b2.company_id
) AS 'Usage_June'
FROM MYTABLE b1
#Group by company in order to add sum of all zones the company is using
group by b1.company_id
order by Usage_June desc;