How to get WeekDay in between two days in SQL server - sql

Question

Please help, I have a below sample data. How to find week days "Tuesday" and count between two days.
CREATE TABLE EmpDetails1 (id INT, name VARCHAR(25),startdate datetime,enddate datetime)
INSERT INTO EmpDetails1 VALUES(1,'TEST','01/01/2016','01/10/2016');
INSERT INTO EmpDetails1 VALUES(2,'TEST','01/01/2016','01/25/2016');
id name startdate enddate
1 Test 1 1/1/16 1/10/16
2 Test 2 1/1/16 1/25/16
output:
date count
1/5/16 1
1/12/16 3
I have tried with below query but not getting correct result
SELECT name,
DATENAME(WEEKDAY, startdate) as w1,
DATENAME(WEEKDAY, enddate) as w2,
startdate,enddate, count(*) OVER(PARTITION BY startdate,enddate) AS CountOfOrders from EmpDetails1 group by startdate , enddate,name

Answer 1

As mentioned already, you need a calendar. You can generate one dynamically but far better to create a static one since it serves so many useful purposes. This is but one of many discussions about how to generate one.
A calendar is just a special form of a tally table and I use Itzik's discussion as a basis for that. Both of these concepts are things you need to understand in most SQL query writing environments.
Once you have a calendar, you simply join your data table to the calendar and filter as needed. I did not understand exactly what you were trying to accomplish so I simply create the set of rows for "Tuesday".
declare #EmpDetails1 table (id int, name varchar(20), startdate date, enddate date);
insert #EmpDetails1 (id, name, startdate, enddate) values
(1, 'Test 1', '20210101', '20210110'),
(2, 'Test 2', '20210116', '20210126');
select emp.*, cal.*, datename(weekday, cal.caldt) as [day of week(eng)]
from #EmpDetails1 as emp
inner join calendar as cal
on cal.caldt between emp.startdate and emp.enddate
and datename(weekday, cal.caldt) = 'Tuesday'
order by emp.id, cal.caldt
;
Fiddle here to demonstrate. I must highlight the lazy usage of * as the column list but this is just a simple demo. Production code should generally always specify the columns needed completely.
If you examine the calendar table discussion, you will see that the day of week can be easily added to the table - it will never change. This will avoid the effort to calculate it in the query.

Answer 2

T-SQL Code:
CREATE PROCEDURE tuesdayCount #id_number INT AS
BEGIN
DECLARE #S_Date DATETIME
DECLARE #E_Date DATETIME
SET #S_Date = (SELECT startdate FROM EmpDetails1 WHERE id = #id_number)
SET #E_Date = (SELECT enddate FROM EmpDetails1 WHERE id = #id_number)
WHILE #S_Date <= #E_Date
IF (FORMAT(#S_Date, '%a') = 'Tue')
INSERT INTO TuesdayDates VALUES(#S_Date, 1)
SET #S_Date = DATEADD(DAY,1, #S_Date)
END
EXECUTE tuesdayCount #id_number=1;
EXECUTE tuesdayCount #id_number=2;
Code Steps:
First line I created a procedure named tuesdayCount with an input parameter(id_number)
Then I declared 2 variables (S_Date and E_Date) with DATETIME data type, then set them equal to startdate and endnote column values in the first row.(Please take note of id_number sp parameter in the where clause.)
Then I defined a while loop and if_ test to ensure the date is really a Tuesday. If that's so, then I inserted the date value(S_Date) into TuesdayDates table which I created myself beforehand to put the result set there. (maybe not so logical; but I did it anyway.)
After defining the sp proc, I called my functions with id_number parameter which is in fact the row number of your data set (EmpDetails1 Table)
Not a perfect solution :) but I hope It helps somehow.