SqlServer:Select and group by Month - sql

Question

I want to write a SQL to count the sales of my last six months, just like the code below.
SELECT
MONTH (pc.createTime) AS MONTH,
SUM (partsModelSum) AS totalSum
FROM
partscontractlinkmodel AS pl
RIGHT JOIN partscontract pc ON pl.partsContractID = pc.partsContractID
AND pc.companyID = 8
AND pc.createTime BETWEEN '2013/11/01 00:00:00'
AND '2014/04/30 23:59:59'
WHERE
pl.partsModelID = 21028
GROUP BY
MONTH (pc.createTime)
ORDER BY
totalSum DESC
AND results is：
month totalSum
4 24
But the problem the problem arises,No sales record month does not appear in the query results, I want there is no sales records in results and a value of 0
like this：
month totalSum
4 24
3 0
2 0
1 0
12 0
11 0
So,How to modify sql solve my problem ;)
thanks

Answer 1

If you have some data every month, you can use conditional aggregation:
SELECT MONTH (pc.createTime) AS MONTH,
SUM(CASE WHEN pl.partsModelID = 21028 THEN partsModelSum END) AS totalSum
FROM partscontract pc LEFT JOIN
partscontractlinkmodel pl
ON pl.partsContractID = pc.partsContractID AND
pc.companyID = 8 AND
pc.createTime BETWEEN '2013/11/01 00:00:00' AND '2014/04/30 23:59:59'
GROUP BY
MONTH(pc.createTime)
ORDER BY totalSum DESC;
If this doesn't work, you need to generate the list of months using a subquery or CTE.

Answer 2

Get a list of month from a table or sub query. Left join the months table/query and partscontract via month(createTime) and month from table/sub-query. Left join partscontract and partscontractlinkmodel like what you did. See below for sample:
;WITH CTE_Month
as
(
SELECT 1 as MonthN
UNION
SELECT 2 as MonthN
UNION
SELECT 3 as MonthN
UNION
SELECT 4 as MonthN
UNION
SELECT 5 as MonthN
UNION
SELECT 6 as MonthN
UNION
SELECT 7 as MonthN
UNION
SELECT 8 as MonthN
UNION
SELECT 9 as MonthN
UNION
SELECT 10 as MonthN
UNION
SELECT 11 as MonthN
UNION
SELECT 12 as MonthN
),
SELECT
N.MonthN AS MONTH,
SUM (ISNULL(partsModelSum,0)) AS totalSum
FROM
CTE_Month M
LEFT JOIN partscontract pc ON MONTH (pc.createTime) = N.MonthN
LEFT JOIN partscontractlinkmodel AS pl
ON pl.partsContractID = pc.partsContractID
AND pc.companyID = 8
AND pc.createTime BETWEEN '2013/11/01 00:00:00'
AND '2014/04/30 23:59:59'
WHERE
pl.partsModelID = 21028
GROUP BY
N.MonthN
ORDER BY
totalSum DESC

Answer 3

You can create a temp table of list of months and use it in the join...may be something like this...
SELECT
MONTH (pc.createTime) AS MONTH,
SUM (partsModelSum) AS totalSum
FROM
(select 1 monthNum union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9 union select 10 union select 11 union select 12 ) MonthList
left join partscontract pc ON MonthList.monthNum = MONTH(pc.createTime)
left join partscontractlinkmodel AS pl ON pc.partsContractID = pl.partsContractID
AND pc.companyID = 8
AND pc.createTime BETWEEN '2013/11/01 00:00:00'
AND '2014/04/30 23:59:59'
WHERE
pl.partsModelID = 21028
GROUP BY
MONTH (pc.createTime)
ORDER BY
totalSum DESC