Using GROUP BY and ORDER BY on an INNER JOIN SQL query - sql

Question

I am using the following query to group work times and expenses for clients from three tables, one for clients, one for work times and one for expenses:
SELECT a.*,
COALESCE(b.totalCount, 0) AS CountWork,
COALESCE(b.totalAmount, 0) AS WorkTotal,
COALESCE(c.totalCount, 0) AS CountExpense,
COALESCE(c.totalAmount, 0) AS ExpenseTotal
FROM clients A
LEFT JOIN
(
SELECT Client,
COUNT(*) totalCount,
SUM(Amount) totalAmount
FROM work_times
WHERE DATE BETWEEN '2013-01-01' AND '2013-02-01'
GROUP BY Client
) b ON a.Client = b.Client
LEFT JOIN
(
SELECT Client,
COUNT(*) totalCount,
SUM(Amount) totalAmount
FROM expenses
WHERE DATE BETWEEN '2013-01-01' AND '2013-02-01'
GROUP BY Client
) c ON a.Client = c.Client
WHERE b.Client IS NOT NULL OR
c.Client IS NOT NULL
You can see the query working in a fiddle here.
I am trying to amend this query so that there is a row for each client for each month sorted by month and then client. I am trying to do so with the following amended query:
SELECT a.*,
COALESCE(b.totalCount, 0) AS CountWork,
COALESCE(b.totalAmount, 0) AS WorkTotal,
COALESCE(c.totalCount, 0) AS CountExpense,
COALESCE(c.totalAmount, 0) AS ExpenseTotal
FROM clients A
LEFT JOIN
(
SELECT Client,
COUNT(*) totalCount,
SUM(Amount) totalAmount,
SUBSTR(Date, 1, 7) as Month
FROM work_times
GROUP BY Month,Client
ORDER BY Month
) b ON a.Client = b.Client
LEFT JOIN
(
SELECT Client,
COUNT(*) totalCount,
SUM(Amount) totalAmount,
SUBSTR(Date, 1, 7) as Month
FROM expenses
GROUP BY Month,Client
ORDER BY Month,Client
) c ON a.Client = c.Client
WHERE b.Client IS NOT NULL OR
c.Client IS NOT NULL
You can see the amended query in action here.
It's not working quite right though. Only one row is returned for Client B even though there is a work time in January 2013 and an expense in February 2013 (so there should be 2 rows) and it appears that the rows are being ordered by Client as opposed to Month. Could someone suggest how to amend the query to get the desired output which for the example on the second fiddle would be:
╔════════╦═══════════╦═══════════╦══════════════╦══════════════╗
║ CLIENT ║ COUNTWORK ║ WORKTOTAL ║ COUNTEXPENSE ║ EXPENSETOTAL ║
╠════════╬═══════════╬═══════════╬══════════════╬══════════════╣
║ A ║ 1 ║ 10 ║ 1 ║ 10 ║
║ B ║ 1 ║ 20 ║ 0 ║ 0 ║
║ A ║ 1 ║ 15 ║ 0 ║ 0 ║
║ B ║ 0 ║ 0 ║ 1 ║ 10 ║
║ C ║ 1 ║ 10 ║ 0 ║ 0 ║
╚════════╩═══════════╩═══════════╩══════════════╩══════════════╝

Answer 1

Unless I am missing something in the requirements, what you need to do is get a list of the clients and the dates and then join that to your subqueries. So your query will be:
SELECT a.*,
COALESCE(b.totalCount, 0) AS CountWork,
COALESCE(b.totalAmount, 0) AS WorkTotal,
COALESCE(c.totalCount, 0) AS CountExpense,
COALESCE(c.totalAmount, 0) AS ExpenseTotal
FROM
(
select distinct c.Client, d.Month
from clients c
cross join
(
select SUBSTR(Date, 1, 7) as Month
from work_times
union
select SUBSTR(Date, 1, 7) as Month
from expenses
) d
) A
LEFT JOIN
(
SELECT Client,
COUNT(*) totalCount,
SUM(Amount) totalAmount,
SUBSTR(Date, 1, 7) as Month
FROM work_times
GROUP BY Month,Client
ORDER BY Month,Client
) b
ON a.Client = b.Client
and a.month = b.month
LEFT JOIN
(
SELECT Client,
COUNT(*) totalCount,
SUM(Amount) totalAmount,
SUBSTR(Date, 1, 7) as Month
FROM expenses
GROUP BY Month,Client
ORDER BY Month,Client
) c
ON a.Client = c.Client
and a.month = c.month
WHERE b.Client IS NOT NULL OR
c.Client IS NOT NULL
order by a.month, a.client
See SQL Fiddle with Demo.
The result is:
| CLIENT | MONTH | COUNTWORK | WORKTOTAL | COUNTEXPENSE | EXPENSETOTAL |
--------------------------------------------------------------------------
| A | 2013-01 | 1 | 10 | 1 | 10 |
| B | 2013-01 | 1 | 20 | 0 | 0 |
| A | 2013-02 | 1 | 15 | 0 | 0 |
| B | 2013-02 | 0 | 0 | 1 | 20 |
| C | 2013-02 | 1 | 10 | 0 | 0 |

Answer 2

If you do an order by in a sub-query, it doesn't matter, because the outer query may (and may need to) re-order the results. You want to add an order by to the outer query.
Your problem is that you are trying to order by the month and client of the B table, and also order by the month and client of the C table. You need to define the order of B.month, B.client, and C.month and put it into an order by for the outer query.
BTW, if you only group by month in the sub-query for the C table, then client is not meaningful. Some databases, like DB2, do not allow you to put an unaggregated field in a select if it is not in the group by.