How do I fetch data grouped by month and year including the period with no data? - sql

Question

Relatively new to SQL and I am stumped on this little issue. This doesn't seem to be very difficult to do, but I just can't seem to figure it out.
I am trying to get a count of transactions from a table, but I can't seem to get sql to get me to show all of the months instead of only the months and the year that the transactions occured in.
Here is the query:
SELECT YEAR(dbo.countproject.trans_date) AS [TransYear]
, MONTH (dbo.countproject.trans_date) AS [TransMonth]
, COUNT(Id) AS TransNum
FROM dbo.countproject
WHERE dbo.countproject.make_name = 'Honda'
AND dbo.countproject.model_name = 'Civic'
AND dbo.countproject.type = 'Sale'
AND dbo.countproject.trans_type LIKE '%%EU'
AND dbo.countproject.mfr = '2000'
GROUP BY YEAR(dbo.countproject.trans_date)
, MONTH(dbo.countproject.trans_date)
ORDER BY YEAR(dbo.countproject.trans_date)
The query returns the following result set:
| TransYear | TransMonth | TransNum |
|-----------|------------|----------|
| 2004 | 1 | 5 |
| 2004 | 3 | 1 |
| 2005 | 4 | 2 |
and so forth....
I am trying to get it to show all the months and years even if the value is NULL.
I tried creating a new table which will have the year and the month as columns to get it to join somehow, but I am lost.
Any help would be appreciated.

Answer 1

If you are using SQL Server 2005 or above, you could use Common Table Expressions (CTE) to get the desired result. Below example shows how you can fetch the results as you had described in the question.
Click here to view the demo in SQL Fiddle.
Description:
Create and insert statements create the table and populates with some sample data. I have created the table based on the query provided in the question.
The statement within the WITH clause is executing a recursive expression. In this case the SELECT above the UNION ALL fetches the minimum and maximum dates available in the table dbo.countproject
Once the minimum date is fetched, the second SELECT statement after the UNION ALL increments the date in 1 month intervals until the recursive expression reaches the maximum date available in the table.
The recursive CTE has produced all the available dates possible. This output is available in the table named alltransactions.
We have to join this CTE output alltransactions with the actual table countproject using LEFT OUTER JOIN since we want to show all years and months even if there are no transactions.
The tables alltransactions and countproject are joined on the year and month parts of the date. The query then applies the necessary filters in the WHERE clause and then groups the data by year and month before ordering it by year and month.
You can notice from the sample data that the earliest date in the table is 2004-07-01 and the latest date is 2005-12-01. Hence the output shows from year 2004 / month 07 till year 2005 / month 12.
Hope that helps.
Script:
CREATE TABLE dbo.countproject
(
id INT NOT NULL IDENTITY
, trans_date DATETIME NOT NULL
, make_name VARCHAR(20) NOT NULL
, model_name VARCHAR(20) NOT NULL
, type VARCHAR(20) NOT NULL
, trans_type VARCHAR(20) NOT NULL
, mfr INT NOT NULL
);
INSERT INTO dbo.countproject (trans_date, make_name, model_name, type, trans_type, mfr) VALUES
('1900-01-01', 'Honda', 'Civic', 'Sale', 'EU', 2000),
('1900-01-01', 'Toyota', 'Corolla', 'Sale', 'EU', 2000),
('2004-07-01', 'Nissan', 'Altima', 'Sale', 'EU', 2000),
('2005-12-01', 'Toyota', 'Camry', 'Sale', 'EU', 2000),
('2004-04-01', 'Ford', 'Focus', 'Sale', 'EU', 2000),
('2005-08-01', 'Honda', 'Civic', 'Sale', 'EU', 2000),
('2005-11-01', 'Toyota', 'Camry', 'Sale', 'EU', 2000),
('2004-08-01', 'Toyota', 'Corolla', 'Sale', 'EU', 2000),
('2005-12-01', 'Honda', 'Civic', 'Sale', 'EU', 2000),
('2004-07-01', 'Honda', 'Civic', 'Sale', 'EU', 2000),
('2004-11-01', 'Honda', 'Civic', 'Sale', 'EU', 2000),
('2005-08-01', 'Honda', 'Civic', 'Sale', 'EU', 2000);
;WITH alltransactions
AS
(
SELECT MIN(trans_date) AS continuousdate
, MAX(trans_date) AS maximumdate
FROM dbo.countproject
WHERE trans_date <> '1900-01-01'
UNION ALL
SELECT DATEADD(MONTH, 1, continuousdate) AS continuousdate
, maximumdate
FROM alltransactions
WHERE DATEADD(MONTH, 1, continuousdate) <= maximumdate
)
SELECT YEAR(at.continuousdate) AS [Year]
, MONTH(at.continuousdate) AS [Month]
, COUNT(cp.trans_date) AS [Count]
FROM alltransactions at
LEFT OUTER JOIN countproject cp
ON YEAR(at.continuousdate) = YEAR(cp.trans_date)
AND MONTH(at.continuousdate) = MONTH(cp.trans_date)
AND cp.make_name = 'Honda'
and cp.model_name = 'Civic'
and cp.type = 'Sale'
and cp.trans_type LIKE '%EU'
and cp.mfr = '2000'
GROUP BY YEAR(at.continuousdate)
, MONTH(at.continuousdate)
ORDER BY [Year]
, [Month];
Output:
Year Month Count
----- ------ -----
2004 4 0
2004 5 0
2004 6 0
2004 7 1
2004 8 0
2004 9 0
2004 10 0
2004 11 1
2004 12 0
2005 1 0
2005 2 0
2005 3 0
2005 4 1
2005 5 0
2005 6 0
2005 7 0
2005 8 2
2005 9 0
2005 10 0
2005 11 0
2005 12 1

Answer 2

You have to use an LEFT or RIGHT OUTER JOIN!
Here is an easy sample: http://www.w3schools.com/sql/sql_join_left.asp
You should get it done by yourself.
Greetings

Answer 3

Alas, the SQL statement can only return the data in the table. If you want all months, you need either a table with the year/month combinations you are intererested in or, preferably, a calendar table with all days and information about them.
With a calendar table, your query have a from clause that looked like:
from
(
select distinct year(date) as yr, month(date) as mon
from calendar c
where date between <earliest> and <latest>
) c
left outer join CountTable ct
on c.yr = year(ct.trans_date)
and c.mon = month(ct.trans_date)