Count each days of week between two dates without loop - sql

Question

I can do it with loop, but if many day is slow. So I need do without loop.
Here is my code:
DECLARE
#FRDT date = '01-SEP-2019'
,#TODT date = '30-SEP-2019'
,#N int
,#SUN int = 0
,#MON int = 0
,#TUE int = 0
,#WED int = 0
,#THU int = 0
,#FRI int = 0
,#SAT int = 0
WHILE #FRDT <= #TODT
BEGIN
SET #N = DATEPART(WEEKDAY, #FRDT)
IF #N = 1
SET #SUN = #SUN + 1
ELSE IF #N = 2
SET #MON = #MON + 1
ELSE IF #N = 3
SET #TUE = #TUE + 1
ELSE IF #N = 4
SET #WED = #WED + 1
ELSE IF #N = 5
SET #THU = #THU + 1
ELSE IF #N = 6
SET #FRI = #FRI + 1
ELSE IF #N = 7
SET #SAT = #SAT + 1
SET #FRDT = DATEADD(DAY, 1, #FRDT)
END
SELECT 1 AS [NO], 'Sunday' AS [DAYNAME], #SUN AS [NUMBEROFDAY]
UNION SELECT 2, 'Monday', #MON
UNION SELECT 3, 'Tuesday', #TUE
UNION SELECT 4, 'Wednesday', #WED
UNION SELECT 5, 'Thursday', #THU
UNION SELECT 6, 'Friday', #FRI
I want to result like code above, but not use loop for better performance.

Answer 1

The date range is 30 days, dividing by 7 gives quotient 4 and remainder 2.
So every day of the week gets 4 and two days need an additional one. These are the ones corresponding to #start_date and the following day in this case.
SQL to implement this approach is below (demo)
SELECT DATENAME(WEEKDAY,base_date),
quotient + IIF(Nums.N < remainder, 1, 0)
FROM (VALUES
(0),
(1),
(2),
(3),
(4),
(5),
(6)) Nums(N)
CROSS APPLY(SELECT 1 + DATEDIFF(DAY,#start_date,#end_date)) DC(day_count)
CROSS APPLY(SELECT DATEADD(DAY, Nums.N, #start_date), day_count/7, day_count% 7) D(base_date, quotient, remainder)
ORDER BY DATEPART(DW,base_date)

Answer 2

You can do it with using recursive CTE as below-
DECLARE #start_date DATE= '01-SEP-2019', #end_date DATE= '30-SEP-2019';
WITH cte
AS (
SELECT #start_date AS date_
UNION ALL
SELECT CAST(DATEADD(day, 1, date_) AS DATE)
FROM cte
WHERE date_ < #end_date
)
SELECT DATEPART(DW,date_) No,
DATENAME(DW,date_) Day_Name,
COUNT(*) Num_Day
FROM cte
GROUP BY DATEPART(DW,date_),DATENAME(DW,date_)
ORDER BY DATEPART(DW,date_)
OPTION(MAXRECURSION 0);
Output-
No Day_Name Num_Day
1 Sunday 5
2 Monday 5
3 Tuesday 4
4 Wednesday 4
5 Thursday 4
6 Friday 4
7 Saturday 4

Answer 3

For such situation you need to have a Number table or Date Table.
In my example I am using a Number table. You can create number table anyway you want and it will help in many situations.
Create Table tblNumber(Number int primary key)
insert into tblNumber (Number) values(1),(2)...... till thousands or millions
Edit: You could generate the numbers for this number table using:
INSERT INTO tblNumber
SELECT TOP 100000 ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS [N]
FROM dbo.syscolumns tb1,dbo.syscolumns tb2
Keep this table permanently as it is useful.
DECLARE #FromDT DATETIME= '2019-09-01';
DECLARE #ToDT DATETIME= '2019-09-30';
SELECT COUNT(*), wkday
FROM
(
SELECT DATEname(weekday, DATEADD(day, number, #FromDT)) wkday
FROM tblNumber
WHERE number BETWEEN DATEPART(day, #FromDT) AND DATEPART(day, #ToDT)
) tbl
GROUP BY wkday;
If you have a Date table then it is more efficient in this situation.