What is the best way to find next n week days - sql

Question

I got the following code from the following question I asked:
Passing in Week Day name to get nearest date in SQL
I need to find next 4 Weekdays based on today's date for corresponding Day-Of-Week in my table ie, if today is 2015-01-24 the result should be 1/24, 1/31, 2/7, 2/14 for Saturdays.
TABLE
SAMPLE QUERY
create table #t
(
jobId int,
personId int,
frequencyVal varchar(10)
);
insert into #t values (1,100,'Mondays'),(2,101,'Saturdays');
WITH cte(n) AS
(
SELECT 0
UNION ALL
SELECT n+1 FROM cte WHERE n < 3
)
select #t.jobId, #t.personId, #t.frequencyVal, STUFF(a.d, 1, 1, '') AS FutureDates
from #t
cross apply (SELECT CASE #t.frequencyVal
WHEN 'SUNDAYS' THEN 1
WHEN 'MONDAYS' THEN 2
WHEN 'TUESDAYS' THEN 3
WHEN 'WEDNESDAYS' THEN 4
WHEN 'THURSDAYS' THEN 5
WHEN 'FRIDAYS' THEN 6
WHEN 'SATURDAYS' THEN 7
END)tranlationWeekdays(n)
cross apply (select ',' + CONVERT(varchar(10), CONVERT(date,dateadd(WEEK, cte.n,CONVERT(DATE, DATEADD(DAY, (DATEPART(WEEKDAY, GETDATE()) + tranlationWeekdays.n) % 7, GETDATE()))))) from cte FOR XML PATH('')) a(d);
drop table #t;
EXPECTED RESULT

Answer 1

Gets the first day of current month.
DECLARE #FIRSTDAY DATE=DATEADD(month, DATEDIFF(month, 0, GETDATE()), 0)
Create the table and insert values
create table #t
(
jobId int,
personId int,
frequencyVal varchar(10)
);
insert into #t values (1,100,'Mondays'),(2,101,'Saturdays');
You can use either of the below queries for your situation.
QUERY 1 : Select the first 4 week of days in current month for particular week day
-- Gets the first day of current month
DECLARE #FIRSTDAY DATE=DATEADD(month, DATEDIFF(month, 0, GETDATE()), 0)
;WITH CTE as
(
-- Will find all dates in current month
SELECT #FIRSTDAY as DATES
UNION ALL
SELECT DATEADD(DAY,1,DATES)
FROM CTE
WHERE DATES < DATEADD(MONTH,1,#FIRSTDAY)
)
,CTE2 AS
(
-- Join the #t table with CTE on the datename+'s'
SELECT jobId,personId,frequencyVal, DATES,
ROW_NUMBER() OVER(PARTITION BY DATENAME(WEEKDAY,CTE.DATES) ORDER BY CTE.DATES) DATECNT
FROM CTE
JOIN #t ON DATENAME(WEEKDAY,CTE.DATES)+'s' = #t.frequencyVal
WHERE MONTH(DATES)= MONTH(GETDATE())
)
-- Converts to CSV and make sure that only 4 days are generated for month
SELECT DISTINCT C2.jobId,C2.personId,frequencyVal,
SUBSTRING(
(SELECT ', ' + CAST(DATEPART(MONTH,DATES) AS VARCHAR(2)) + '/' +
CAST(DATEPART(DAY,DATES) AS VARCHAR(2))
FROM CTE2
WHERE C2.jobId=jobId AND C2.personId=personId AND DATECNT<5
ORDER BY CTE2.DATES
FOR XML PATH('')),2,200000) futureDates
FROM CTE2 C2
SQL FIDDLE
For example, in Query1 the nearest date(here we take example as Saturday) of
2015-Jan-10 will be 01/03,01/10,01/17,01/24
2015-Jan-24 will be 01/03,01/10,01/17,01/24
QUERY 2 : Select nearest 4 week of days in current month for particular week day
-- Gets the first day in current month
DECLARE #FIRSTDAY DATE=DATEADD(month, DATEDIFF(month, 0, GETDATE()), 0)
;WITH CTE as
(
-- Will find all dates in current
SELECT CAST(#FIRSTDAY AS DATE) as DATES
UNION ALL
SELECT DATEADD(DAY,1,DATES)
FROM CTE
WHERE DATES < DATEADD(MONTH,1,#FIRSTDAY)
)
,CTE2 AS
(
-- Join the #t table with CTE on the datename+'s'
SELECT jobId,personId,frequencyVal,DATES,
-- Get week difference for each weekday
DATEDIFF(WEEK,DATES,GETDATE()) WEEKDIFF,
-- Count the number of weekdays in a month
COUNT(DATES) OVER(PARTITION BY DATENAME(WEEKDAY,CTE.DATES)) WEEKCOUNT
FROM CTE
JOIN #t ON DATENAME(WEEKDAY,CTE.DATES)+'s' = #t.frequencyVal
WHERE MONTH(DATES)= MONTH(GETDATE())
)
-- Converts to CSV and make sure that only nearest 4 week of days are generated for month
SELECT DISTINCT C2.jobId,C2.personId,frequencyVal,
SUBSTRING(
(SELECT ', ' + CAST(DATEPART(MONTH,DATES) AS VARCHAR(2)) + '/' +
CAST(DATEPART(DAY,DATES) AS VARCHAR(2))
FROM CTE2
WHERE C2.jobId=jobId AND C2.personId=personId AND C2.frequencyVal=frequencyVal AND
((WEEKDIFF<3 AND WEEKDIFF>-3 AND WEEKCOUNT = 5) OR WEEKCOUNT <= 4)
ORDER BY CTE2.DATES
FOR XML PATH('')),2,200000) futureDates
FROM CTE2 C2
SQL FIDDLE
For example, in Query2 the nearest date(here we take example as Saturday) of
2015-Jan-10 will be 01/03,01/10,01/17,01/24
2015-Jan-24 will be 01/10,01/17,01/24,01/31
QUERY 3 : Select next 4 week's dates for particular week day irrelevant of month
;WITH CTE as
(
-- Will find all dates in current month
SELECT CAST(GETDATE() AS DATE) as DATES
UNION ALL
SELECT DATEADD(DAY,1,DATES)
FROM CTE
WHERE DATES < DATEADD(DAY,28,GETDATE())
)
,CTE2 AS
(
-- Join the #t table with CTE on the datename+'s'
SELECT jobId,personId,frequencyVal, DATES,
ROW_NUMBER() OVER(PARTITION BY DATENAME(WEEKDAY,CTE.DATES) ORDER BY CTE.DATES) DATECNT
FROM CTE
JOIN #t ON DATENAME(WEEKDAY,CTE.DATES)+'s' = #t.frequencyVal
)
-- Converts to CSV and make sure that only 4 days are generated for month
SELECT DISTINCT C2.jobId,C2.personId,frequencyVal,
SUBSTRING(
(SELECT ', ' + CAST(DATEPART(MONTH,DATES) AS VARCHAR(2)) + '/' +
CAST(DATEPART(DAY,DATES) AS VARCHAR(2))
FROM CTE2
WHERE C2.jobId=jobId AND C2.personId=personId AND C2.frequencyVal=frequencyVal
AND DATECNT < 5
ORDER BY CTE2.DATES
FOR XML PATH('')),2,200000) futureDates
FROM CTE2 C2
SQL FIDDLE
The following would be the output if the GETDATE() (if its Saturday) is
2015-01-05 - 1/10, 1/17, 1/24, 1/31
2015-01-24 - 1/24, 1/31, 2/7, 2/14

Answer 2

This is a simpler way I think, and I think it fits your requirements
Note that I have changed your frequency_val column to an integer that represents the day of the week from SQL servers perspective and added a calculated column to illustrate how you can easily derive the day name from that.
/*************************************************/
--Set up our sample table
/*************************************************/
declare #t table
(
jobId int,
personId int,
--frequencyVal varchar(10) -- why store a string when a tiny int will do.
frequency_val tinyint,
frequency_day as datename(weekday,frequency_val -1) + 's'
)
insert into #t
values
(1,100,1),--'Mondays'),
(2,101,6),--'Saturdays');
(3,101,7),--'Sundays');
(4,100,2)--'Tuesdays'),
--select * from #t
/*************************************************/
--Declare & initialise variables
/*************************************************/
declare #num_occurances int = 4
declare #from_date date = dateadd(dd,3,getdate()) -- this will allow you to play with the date simply by changing the increment value
/*************************************************/
-- To get a row for each occurance
/*************************************************/
;with r_cte (days_ahead, occurance_date)
as (select 0, convert(date,#from_date,121)
union all
select r_cte.days_ahead +1, convert(date,dateadd(DD, r_cte.days_ahead+1, #from_date),121)
from r_cte
where r_cte.days_ahead < (7 * #num_occurances) -1
)
select t.*, r_cte.occurance_date
from
#t t
inner join r_cte
on DATEPART(WEEKDAY, dateadd(dd,##DATEFIRST - 1 ,r_cte.occurance_date)) = t.frequency_val
/*************************************************/
--To get a single row with a CSV of every occurance
/*************************************************/
;with r_cte (days_ahead, occurance_date)
as (select 0, convert(date,#from_date,121)
union all
select r_cte.days_ahead +1, convert(date,dateadd(DD, r_cte.days_ahead+1, #from_date),121)
from r_cte
where r_cte.days_ahead < (7 * #num_occurances) -1
)
select
t.*,
STUFF( (select ', '
+ convert(varchar(2),datepart(month,occurance_date),0) + '/'
+ convert(varchar(2),datepart(day,occurance_date),0) as occurance
from r_cte
where DATEPART(WEEKDAY, dateadd(dd,##DATEFIRST - 1 ,r_cte.occurance_date)) = t.frequency_val
FOR XML PATH (''),TYPE).value('.','varchar(30)')
,1,2,'') occurance_date -- rest of STUFF() function
from
#t t