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SQL PUZZLE | Missing Dates for each month ?? | SQL Interview Question

In this puzzle you have to find out the missing dates for each month. Please check out sample input and expected output. The should be generic in nature.

Sample Input

Month Date
201806 1
201806 2
201806 5
201806 6
201806 8
201807 1
201807 4
201807 6
201809 1
201809 2

Expected output

Month MissingDates
201806 3
201806 4
201806 7
201807 2
201807 3
201807 5

Script – DDL and INSERT sample data

--

CREATE TABLE Dts
(
	 [Month] INT
	,[Date] INT
)
GO

INSERT INTO Dts VALUES
(201806,1),
(201806,2),
(201806,5),
(201806,6),
(201806,8),
(201807,1),
(201807,4),
(201807,6),
(201809,1),
(201809,2)
GO

SELECT * FROM Dts
GO

--

SOLUTION – 1

--

;WITH SingleDigits(Number) AS
(
    SELECT Number
    FROM (VALUES (1), (2), (3), (4), (5), (6), (7), (8),
    (9), (0)) AS X(Number)
)
,Series AS
(
    SELECT (d1.Number+1) + (10*d2.Number) Number
    from
    SingleDigits as d1,
    SingleDigits as d2
),
CTE1 AS 
( 
	SELECT [Month] , MIN([Date]) MinDt, MAX([Date]) Maxdt 
	FROM Dts 
	GROUP BY [Month]
)
SELECT c.Month [Month], s.Number MissingDates FROM CTE1 c
INNER JOIN Series s on number >= MinDt AND number <= Maxdt
LEFT JOIN Dts dt on s.Number = dt.[date] AND c.[month] = dt.[month]
WHERE dt.[date] IS NULL

--

OUTPUT – 1

--

Month       MissingDates
----------- ------------
201806      3
201806      4
201806      7
201807      2
201807      3
201807      5

(6 rows affected)

--

Enjoy 🙂

Please add comment(s) if you have one or multiple solutions in mind. Thank You.

Pawan Khowal

Pawan is a SQL Server Developer. If you need any help in writing code/puzzle or training please email at – pawankkmr”AT”gmail.com. Meanwhile please go throgh the top pages from his blog.

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