Find missing period and determine whether consecutive before - sql

Question

I am currently working on a requirement to find the missing period and then determine whether it was consecutive before the missing period
Following is my sample table structure.
First step: In the following sample table look at last 6 months (2014 7 - 2014 12). Its missing two months 8 & 11. Take the first instance 8.
Second step: Go back 6 months from the first instance missing - (2014 2- 2014 7) - see whether they are missing any months. If No (everything is consecutive) - Select/Include this record if Yes (missing some months) - don't select this record.
Year Month
2014 1
2014 2
2014 3
2014 4
2014 5
2014 6
2014 7
2014 9
2014 10
2014 12
I can select last 6 records and partition by row number and see whether its missing any. But I am not sure how to find if its consecutive and also select the missing period.
I am trying to do as much filtration in Transact-SQL so that I can focus on other validations on c#.
Query I created to find first period missing(not complete)
SELECT f.TYEAR,f.TMONTH, f.TMONTH+1 AS MISSING FROM #TEMPTABLE AS F
LEFT OUTER JOIN #TEMPTABLE AS F2 ON f.TMONTH+1 = f2.TMONTH
WHERE f2.TAXPERIOD IS NULL
Note: The above example can span b/w two calendar years. 2013 mm - 2014 mm

Answer 1

This one has been tested, I've spent some time on it, please let me know if you're happy with the result and vote if yes, cheers :-) PS: The table dbo.Months_and_Years contains your data (with the 2 missing months)
CREATE TABLE dbo.Test_Table (
[Year] SMALLINT,
[Month] TINYINT
);
INSERT INTO dbo.Test_Table
VALUES
(2014, 1),
(2014, 2),
(2014, 3),
(2014, 4),
(2014, 5),
(2014, 6),
(2014, 7),
(2014, 9),
(2014, 10),
(2014, 12);
DECLARE #MinValue TINYINT = 1
DECLARE #MaxValue TINYINT = 100
WHILE #MinValue < = #MaxValue
BEGIN
DECLARE #Missing_Month TINYINT = (
SELECT TOP 1 A.RowID
FROM (
SELECT DENSE_RANK() OVER ( ORDER BY [month]) AS RowID ,
*
FROM dbo.Test_Table
) AS A
WHERE A.RowID <> A.[Month]
)
SELECT #Missing_Month
IF #Missing_Month IS NULL
BREAK
ELSE
INSERT INTO dbo.Test_Table
VALUES (2014, #Missing_Month)
SET #MinValue = #MinValue + 1
END
-- Check your results ---
SELECT A.*
FROM dbo.Test_Table AS A
LEFT JOIN dbo.Months_and_Years AS B ON A.[Month] = B.[Month]
WHERE B.[Month] IS NULL;

Answer 2

I think below code should work, though I've not tested it properly. But you will get the idea -
DECLARE #TmpBaseTable TABLE ([Year] SMALLINT, [Month] TINYINT)
DECLARE #TmpSixMonthTable TABLE (TmpYear SMALLINT, TmpMonth TINYINT)
DECLARE #TmpDate DATE
DECLARE #MissingYear SMALLINT
DECLARE #MissingMonth TINYINT
DECLARE #TmpCount TINYINT
INSERT INTO #TmpBaseTable ([Year], [Month])
SELECT 2014, 1 UNION ALL
SELECT 2014, 2 UNION ALL
SELECT 2014, 3 UNION ALL
SELECT 2014, 4 UNION ALL
SELECT 2014, 5 UNION ALL
SELECT 2014, 6 UNION ALL
SELECT 2014, 7 UNION ALL
SELECT 2014, 8 UNION ALL
SELECT 2014, 9 UNION ALL
SELECT 2014, 10 UNION ALL
SELECT 2014, 11 UNION ALL
SELECT 2014, 12 UNION ALL
SELECT 2015, 1 UNION ALL
SELECT 2015, 3 UNION ALL
SELECT 2015, 4
SELECT TOP 1 #TmpDate = CAST(CAST(tmpYear AS VARCHAR) + '-' + CAST(tmpMonth AS VARCHAR) + '-' + CAST(1 AS VARCHAR) AS DATE)
FROM
(
SELECT ROW_NUMBER() OVER(ORDER BY [Year], [Month]) AS RowID, [Month] AS tmpMonth, [Year] AS tmpYear
FROM #TmpBaseTable
)
tmp ORDER BY RowID DESC
INSERT INTO #TmpSixMonthTable (TmpMonth, TmpYear)
SELECT DATEPART(MONTH, DATEADD (MONTH, -5, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -5, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -4, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -4, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -3, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -3, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -2, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -2, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -1, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -1, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -0, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -0, #TmpDate))
SELECT TOP 1 #MissingMonth = tmpSix.TmpMonth, #MissingYear = tmpSix.TmpYear FROM #TmpSixMonthTable tmpSix
LEFT OUTER JOIN #TmpBaseTable tmpBase ON tmpSix.TmpMonth = tmpBase.[Month] AND tmpSix.TmpYear = tmpBase.[Year]
WHERE tmpBase.[Year] IS NULL
SET #TmpDate = CAST(CAST(#MissingYear AS VARCHAR) + '-' + CAST(#MissingMonth AS VARCHAR) + '-' + CAST(1 AS VARCHAR) AS DATE)
DELETE FROM #TmpSixMonthTable
INSERT INTO #TmpSixMonthTable (TmpMonth, TmpYear)
SELECT DATEPART(MONTH, DATEADD (MONTH, -6, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -6, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -5, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -5, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -4, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -4, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -3, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -3, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -2, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -2, #TmpDate)) UNION ALL
SELECT DATEPART(MONTH, DATEADD (MONTH, -1, #TmpDate)), DATEPART(YEAR, DATEADD (MONTH, -1, #TmpDate))
SELECT #TmpCount = COUNT(1) FROM #TmpSixMonthTable tmp1
INNER JOIN #TmpBaseTable tmp2 ON tmp1.TmpMonth = tmp2.[Month] AND tmp1.TmpYear = tmp2.[Year]
IF(#TmpCount = 6)
BEGIN
SELECT tmp2.[Month], tmp2.[Year] FROM #TmpSixMonthTable tmp1
INNER JOIN #TmpBaseTable tmp2 ON tmp1.TmpMonth = tmp2.[Month] AND tmp1.TmpYear = tmp2.[Year]
END
There can be a smarter way than this :)