SQL: Repeat patterns between date range - sql

Question

DECLARE
#startDate date = '2020-07-03'
#endDate date = 2020-07-06'
I have a tabe as below
---------------------------------------------------------
|EmployeeID | EmpName |Pattern | Frequency |
---------------------------------------------------------
| 11 | X | 1,2,3 | 1 |
| 12 | Y | 4,5 | 1 |
| 13 | Y | 1,2 | 3 |
| 14 | Z | 1,2 | 2 |
---------------------------------------------------------
AND I want to generate dates between given date range.
WANT result table as bellows:
--------------------------------
| EmpId | Dates | Pattern |
--------------------------------
| 11 |2020-07-03 | 1 |
| 11 |2020-07-04 | 2 |
| 11 |2020-07-05 | 3 |
| 11 |2020-07-06 | 1 |
| 12 |2020-07-03 | 4 |
| 12 |2020-07-04 | 5 |
| 12 |2020-07-05 | 4 |
| 12 |2020-07-06 | 5 |
| 13 |2020-07-03 | 1 |
| 13 |2020-07-04 | 1 |
| 13 |2020-07-05 | 1 |
| 13 |2020-07-06 | 2 |
| 14 |2020-07-03 | 1 |
| 14 |2020-07-04 | 1 |
| 14 |2020-07-05 | 2 |
| 14 |2020-07-06 | 2 |
Generate the dates as per given date range for each employee and repeat the pattern for each employee as per their pattern and frequency(days).
means as per frequency(days) pattern will change.
What I have acheived :
Able to generate the records for each employees between the given date range.
What I am not able to get:
I am not able to repeat the pattern based on the frequency for each employee between the date range.
I am able achieve everything but need little help while repeating the pattern based on frequency.*
Note:
Data are storing in this way only.. now I won't change existing schema...

Answer 1

I've came up with this. It's basically a splitter, a tally table and some logic.
Joining (Frequency)-Amount of Tally-datasets with the splitted pattern for the correct amount of pattern-values. Sorting them by their position in the pattern-string.
Join everything together and repeat the pattern by using modulo.
DECLARE #t TABLE( EmployeeID INT
, EmpName VARCHAR(20)
, Pattern VARCHAR(255)
, Frequency INT )
DECLARE #startDate DATE = '2020-07-03'
DECLARE #endDate DATE = '2020-07-09'
INSERT INTO #t
VALUES (11, 'X', '1,2,3', 1),
(12, 'Y', '4,5', 1),
(13, 'Y', '1,2', 3),
(14, 'Z', '1,2', 2)
DECLARE #delimiter CHAR(1) = ',';
WITH split(Txt
, i
, elem
, EmployeeID)
AS (SELECT STUFF(Pattern, 1, CHARINDEX(#delimiter, Pattern+#delimiter+'~'), '')
, 1
, CAST(LEFT(Pattern, CHARINDEX(#delimiter, Pattern+#delimiter+'~')-1) AS VARCHAR(MAX))
, EmployeeID
FROM #t
UNION ALL
SELECT STUFF(Txt, 1, CHARINDEX(#delimiter, Txt+#delimiter+'~'), '')
, i + 1
, CAST(LEFT(Txt, CHARINDEX(#delimiter, Txt+#delimiter+'~')-1) AS VARCHAR(MAX))
, EmployeeID
FROM split
WHERE Txt > ''),
E1(N) AS (SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1), --10E+1 or 10 rows
E2(N) AS (SELECT 1 FROM E1 AS a, E1 AS b), --10E+2 or 100 rows
E4(N) AS (SELECT 1 FROM E2 AS a, E2 AS b), --10E+4 or 10,000 rows
E8(N) AS (SELECT 1 FROM E4 AS a , E4 AS b), --10E+8 or 100,000,000 rows
PatternXFrequency(EmployeeID
, Sort
, elem)
AS (SELECT split.EmployeeID
, ROW_NUMBER() OVER(PARTITION BY split.EmployeeID ORDER BY i) - 1
, elem
FROM split
INNER JOIN #t AS t ON t.EmployeeID = split.EmployeeID
CROSS APPLY (SELECT TOP (t.Frequency) 1
FROM E8
) AS Freq(Dummy))
SELECT EmployeeID
, DATEADD(DAY, i_count, #startDate) AS Dates
, elem
FROM (SELECT DATEDIFF(DAY, #startDate, #endDate) + 1) AS t_datediff(t_days)
CROSS APPLY (SELECT TOP (t_days) ROW_NUMBER() OVER(ORDER BY (SELECT 0) ) - 1 FROM E8
) AS t_dateadd(i_count)
CROSS APPLY (SELECT PatternXFrequency.*
FROM (SELECT DISTINCT EmployeeID FROM #t) AS t(EmpID)
CROSS APPLY (SELECT COUNT(Sort)
FROM PatternXFrequency
WHERE EmployeeID = EmpID
) AS EmpPattern(sortCount)
CROSS APPLY (SELECT *
FROM PatternXFrequency
WHERE EmployeeID = EmpID
AND Sort = ((i_count % sortCount))
) AS PatternXFrequency
) AS t
ORDER BY t.EmployeeID
, Dates

Answer 2

This isn't particularly pretty, but it avoids the recursion of a rCTE, so should provide a faster experience. As STRING_SPLIT still doesn't know what ordinal position means, we have to use something else here; I use DelimitedSplit8k_LEAD.
I also assume your expected results are wrong, as they stop short of your end date (20200709). This results in the below:
CREATE TABLE dbo.YourTable (EmployeeID int,
EmpName char(1),
Pattern varchar(8000), --This NEEDS fixing
Frequency tinyint);
INSERT INTO dbo.YourTable
VALUES(11,'X','1,2,3',1),
(12,'Y','4,5',1),
(13,'Y','1,2',3),
(14,'Z','1,2',2);
GO
DECLARE #StartDate date = '20200703',
#EndDate date = '20200709';
WITH CTE AS(
SELECT *,
MAX(ItemNumber) OVER (PARTITION BY EmployeeID) AS MaxItemNumber
FROM dbo.YourTable YT
CROSS APPLY dbo.DelimitedSplit8K_LEAD(YT.Pattern,',') DS),
N AS(
SELECT N
FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL))N(N)),
Tally AS(
SELECT TOP (SELECT DATEDIFF(DAY,#startDate, #EndDate)+1)
ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) - 1 AS I
FROM N N1, N N2, N N3) --1000 Rows
SELECT C.EmployeeID,
DATEADD(DAY,T.I, #StartDate),
C.Item
FROM CTE C
JOIN Tally T ON ISNULL(NULLIF((T.I +1) % C.MaxItemNumber,0),C.MaxItemNumber) = C.ItemNumber
ORDER BY EmployeeID,
T.I;
GO
DROP TABLE dbo.YourTable;

Answer 3

Like mentioned in the comments fix your data model.
Your output pattern is a little bit strange.
But is it something like this you are looking for?
DECLARE #startDate date = '2020-07-03'
DECLARE #endDate date = '2020-07-09'
DECLARE #Dates TABLE([Date] Date)
;WITH seq(n) AS
(
SELECT 0 UNION ALL SELECT n + 1 FROM seq
WHERE n < DATEDIFF(DAY, #StartDate, #endDate)
)
INSERT INTO #Dates ([Date])
SELECT DATEADD(Day,n, cast(GetDate() as date)) Date
FROM seq
ORDER BY n
OPTION (MAXRECURSION 0);
SELECT e.EmployeeId, d.Date, x.Value Pattern
FROM Employee e
CROSS APPLY STRING_SPLIT(e.Pattern, ',') x
INNER JOIN #Dates d on 1=1
-- Correct for the first iteration of the pattern
AND DATEDIFF(DAY, DATEADD(DAY, -1, #StartDate), d.Date) = x.Value