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SQL Server: Determining Whether a Date is a Business Day

Nov 9, 2001

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For the program to be useful in all regional settings, you have to check for the @@DATEFIRST setting. Keep in mind, though, that as you change the @@DATEFIRST value, weekday numbers change as well.

For instance, if you decide to start the week on Saturday instead of Sunday, you'll get a different result with the same query as above:

SET DATEFIRST 6
SELECT DATEPART(WEEKDAY, '9/30/01')

Result:
----------- 
2

Therefore, to determine whether a particular date happens to be a business day, you need to account for each possible value of @@DATEFIRST and respective values for each weekday returned by the DATEPART function. The global variable @@DATEFIRST can take on any value between 1 and 7. You can investigate how the DATEPART function values change as you modify the value of @@DATEFIRST by executing the following code:

SET NOCOUNT ON   -- turn off counting of rows

-- create a table variable to store weekday names and numbers:
DECLARE @temp_table TABLE (
weekday_name VARCHAR(20), 
weekday_number TINYINT, 
DATEFIRST_value TINYINT)

-- declare and populate variables:
DECLARE @date SMALLDATETIME, @n TINYINT, @m TINYINT
SELECT @date = '9/30/01', @n = 1, @m = 1

/* run through all possible values of @@DATEFIRST and find
** appropriate weekday numbers:
*/

WHILE @n < 8
BEGIN
SET DATEFIRST @n
   WHILE @m < 8
   BEGIN
   INSERT @temp_table
   SELECT DATENAME(WEEKDAY, DATEADD(dd, @m, @date)), 
   DATEPART(WEEKDAY, DATEADD(dd, @m, @date)), 
   @@DATEFIRST
   SELECT @m = @m + 1
   END
SELECT @n = @n + 1, @m = 1
END

-- return the results:
SELECT * FROM @temp_table

Table 2 shows the results.

Table 2 Output of the Query

`weekday_name`	`weekday_number`	`DATEFIRST_value`
Monday	1	1
Tuesday	2	1
Wednesday	3	1
Thursday	4	1
Friday	5	1
Saturday	6	1
Sunday	7	1
Monday	7	2
Tuesday	1	2
Wednesday	2	2
Thursday	3	2
Friday	4	2
Saturday	5	2
Sunday	6	2
Monday	6	3
Tuesday	7	3
Wednesday	1	3
Thursday	2	3
Friday	3	3
Saturday	4	3
Sunday	5	3
Monday	5	4
Tuesday	6	4
Wednesday	7	4
Thursday	1	4
Friday	2	4
Saturday	3	4
Sunday	4	4
Monday	4	5
Tuesday	5	5
Wednesday	6	5
Thursday	7	5
Friday	1	5
Saturday	2	5
Sunday	3	5
Monday	3	6
Tuesday	4	6
Wednesday	5	6
Thursday	6	6
Friday	7	6
Saturday	1	6
Sunday	2	6
Monday	2	7
Tuesday	3	7
Wednesday	4	7
Thursday	5	7
Friday	6	7
Saturday	7	7
Sunday	1	7

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