Simple SQL Server COUNT query (counting changes to values in a column) - sql

Question

I have a table with columns: MONTH, YEAR, PROJECT_ID, STATUS.
Status can be:
R (red).
A (amber).
G (green).
N (not started).
C (completed).
I want to know how many projects completed in a given month i.e. :
where STATUS changed from anything that is NOT C to C;
It sounds simple...!
It's easy to find when any given project completed with:
SELECT TOP 1 MONTH,YEAR,PROJECT_ID FROM Table WHERE PROJECT_ID=9236 AND RAG='C'
ORDER BY YEAR ASC, MONTH ASC
But given year = 2011 and month = 8 (for example), I have no idea how to find the number of projects that had status='C' for the first time that month. Any ideas?
Edit: projects are still included as rows with status='C' after they complete, so I can't just count the Cs as that will return the number of projects that completed in this AND previous months (hence the chronological ordering and select top 1).
Sample data for 10/2010 to 01/2011 months:
Month | Year | Project | Status
-------------------------------
10 | 2010 | A | G
11 | 2010 | A | C
12 | 2010 | A | C
1 | 2011 | A | C
10 | 2010 | B | R
11 | 2010 | B | R
12 | 2010 | B | R
1 | 2011 | B | R
10 | 2010 | C | G
11 | 2010 | C | G
12 | 2010 | C | G
1 | 2011 | C | C
10 | 2010 | D | A
11 | 2010 | D | C
12 | 2010 | D | C
1 | 2011 | D | C
^ Projects A and D was completed in 11/2010. Project B hasn't changed to completed in any of the four months shown. Project C was completed in 01/2011. {Month,Year,Project} is the primary key.
So, inputs and outputs would be:
10/2010 => 0
11/2010 => 2 (because of A and D)
12/2010 => 0
1/2011 => 1 (because of C)

Answer 1

This will give you the counts you are looking for
select p1.mm,p1.yyyy,COUNT(*)
from projs p1
join (select projid,MIN(yyyy*100+mm) as closedOn from projs
where stat='c' group by projId) xx
on xx.projId=p1.projId and p1.yyyy*100+p1.mm=xx.closedOn
where p1.stat='c'
group by p1.mm,p1.yyyy
The inner query determines the date the project closed, so you are finding all projects which closed this month...

Answer 2

There you go
WITH
src(month, year, project, status) AS (
SELECT 10,2010,'A','G' UNION ALL
SELECT 11,2010,'A','C' UNION ALL
SELECT 12,2010,'A','C' UNION ALL
SELECT 1,2011,'A','C' UNION ALL
SELECT 10,2010,'B','R' UNION ALL
SELECT 11,2010,'B','R' UNION ALL
SELECT 12,2010,'B','R' UNION ALL
SELECT 1,2011,'B','R' UNION ALL
SELECT 10,2010,'C','G' UNION ALL
SELECT 11,2010,'C','G' UNION ALL
SELECT 12,2010,'C','G' UNION ALL
SELECT 1,2011,'C','C' UNION ALL
SELECT 10,2010,'D','A' UNION ALL
SELECT 11,2010,'D','C' UNION ALL
SELECT 12,2010,'D','C' UNION ALL
SELECT 1,2011,'D','C'),
src_date (date, project, status) AS (
SELECT date = CONVERT(DATETIME, CONVERT(VARCHAR, year * 100 + month) + '01'), project, status
FROM src
)
SELECT month = CONVERT(VARCHAR, YEAR(alldates.date)) + '/' + CONVERT(VARCHAR, MONTH(alldates.date)),
projects = ISNULL(cnt.value,0)
FROM (
SELECT DISTINCT date
FROM src_date
) alldates
LEFT JOIN
(
SELECT date = min_date, value = COUNT(*)
FROM
(
SELECT project, min_date = MIN(date)
FROM src_date
WHERE status = 'C'
GROUP BY project
) mins
GROUP BY min_date
) cnt
ON alldates.date = cnt.date

Answer 3

SELECT
distinctMonths.month,
distinctMonths.year,
count(countProjects.project) as numChanges
FROM
(
SELECT DISTINCT
month, year
FROM
Table
) as distinctMonths -- need to get all months available, independent of the project status, in case there were not an complete ones during a given month
LEFT OUTER JOIN
(
SELECT
Month, Year, Project
FROM
Table
WHERE
status = 'C' AND
NOT EXISTS ( -- this will filter out our result set to only include the earliest instance of the given project's complete status
SELECT
1
FROM
Table t2
WHERE
t2.project = Table.project AND
t2.status = 'C' AND
( -- this will convert the date fragments into proper date values, that can be compared easily
cast(
cast(t2.year as varchar) + '-' + cast(t2.month as varchar) + '-1'
as datetime)
<
cast(
cast(table.year as varchar) + '-' + cast(table.month as varchar) + '-1'
as datetime)
)
)
) as countProjects ON
distinctMonths.month = countProjects.month AND
distinctMonths.year = countProjects.year
GROUP BY
distinctMonths.month,
distinctMonths.year
ORDER BY
distinctMonths.year,
distinctMonths.month

Answer 4

I like to use this function: lead() over().
If you have, for example, this select:
select Month, Year, Project, Status
from youTable
where 1 = 1 --if you have any condition
I find next value of "status" column with lead() function and I compare with the current one so :
select count(1) as number from
(select lead(Status) over(order by Project) as nextStatus, Month, Year, Project, Status
from youTable
where 1=1) as tmp
where tmp.nextStatus <> tmp.Status
now, in number I have the numbers of changed value into "Status" column