SQL: Getting a row for each passing month up to date - sql

Question

I have a table that stores defects.
Each defect has a detection date and a closing date.
I want to extract the info for each month up to current date, about the number of open defects in that month.
For example, lets assume these are all the defects I have in my DB:
defect 1 - Detected in (01-01-2014) , Closed in (04-03-2014)
defect 2 - Detected in (07-02-2014) , Closed in (null) (still open)
I'd like to extract the info as follows:
01-01-2014 - 1 open defect (defect 1 was created)
01-02-2014 - 2 open defects (defect 2 was created)
01-03-2014 - 1 open defect (defect 1 was closed this month)
01-04-2014 - 1 open defect (defect 2 was never closed so I would get entries up to today)
...
...
01-02-2015 - 1 open
Is there a way to get this info with a single query without using functions?

Answer 1

Avoiding the question of "why no functions", it is possible to go N months back (limits apply) with the query below. Just replace "16" in "WHERE n < 16" with the number of months back you want to evaluate
; WITH Numbers (n) AS (
SELECT 1
UNION ALL
SELECT n + 1
FROM Numbers
WHERE n < 16
)
, NextMonth (dt) AS (
SELECT CAST( CAST( DATEPART(YEAR,GETDATE()) AS VARCHAR ) + '-' + CAST( DATEPART(MONTH,GETDATE())+1 AS VARCHAR ) + '-1' AS DATETIME )
)
, PriorMonths (dt) AS (
SELECT DATEADD( MONTH, -1 * n, dt )
FROM NextMonth
CROSS JOIN Numbers
), RawData ( y, m, DateOpened ) AS (
SELECT DATEPART( YEAR, dt )
, DATEPART( MONTH, dt )
, t.DateOpened
FROM PriorMonths AS pm
LEFT JOIN #t AS t
ON DATEADD(MONTH,-1,t.DateOpened) < dt
AND (DATEADD(MONTH,-1,t.DateClosed) >= dt OR t.DateClosed IS NULL)
)
SELECT y, m, COUNT(DateOpened)
FROM RawData
GROUP BY y, m
ORDER BY y DESC, m DESC

Answer 2

First I want to point out that I've used MS SQL Server T-SQL functions DATEADD(), DATEDIFF(), and GETDATE() - there should be equivalents in whatever flavour of SQL you want to use.
The variable #startDate should be set to the start of the range on which you want to report.
DECLARE #startDate DATE;
DECLARE #endDate DATE;
SET #startDate = '20140101';
SET #endDate = DATEADD(m, DATEDIFF(m, 0, GETDATE()), 0);
WITH Dates (dEnd, dStart) AS (
SELECT DATEADD(M, 1, #endDate), #endDate
UNION ALL
SELECT DATEADD(M, -1, dEnd), DATEADD(M, -1, dStart)
FROM Dates
WHERE dEnd > #startDate
)
SELECT dStart AS 'Month start', COUNT(Defects.reportedDate) AS 'Open defects'
FROM Dates
LEFT OUTER JOIN Defects ON
Defects.reportedDate < dEnd AND (Defects.resolvedDate IS NULL OR Defects.resolvedDate > dStart)
GROUP BY dStart
ORDER BY dStart;