How can I calculate the number of specific weekdays within a date range using TSQL?

Calculating the Number of Specific Weekdays within a Date Range

Determining the number of specific weekdays, such as Tuesdays, between two dates can be a common task in data analysis. This problem can be effectively solved using Transact-SQL (TSQL).

To calculate the number of Tuesdays between two dates, a modified approach is recommended, as TSQL does not have a direct function for determining the day of the week as an integer.

The following code snippet outlines the steps:

1. Declare the starting and ending dates as datetime variables:

   declare @from datetime= '3/1/2013'
   declare @to datetime  = '3/31/2013'

2. Use the datediff() function to determine the difference between the dates in days. Subtract 6 from the ending date to align with Sunday, which is considered day 0 in TSQL:

   datediff(day, -6, @to)

3. Divide the result by 7 to get the number of complete weeks (containing each day of the week once) between the dates:

   datediff(day, -6, @to)/7

4. Subtract the same calculation from the starting date to determine which day of the week the starting date falls on:

   datediff(day, -6, @from)/7

5. Subtract the result of step 4 from the result of step 3 to get the number of instances of the specific day (Tuesday, in this case) between the dates:

   datediff(day, -6, @to)/7-datediff(day, -6, @from)/7

By following these steps, you can efficiently calculate the number of Tuesdays or any other specific weekday between two dates using TSQL.

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