How to Efficiently Determine the Number of Days in a Month Using SQL Server?

Determining the Number of Days in a Month in SQL Server

Calculating the number of days in a month is a common task in database operations. SQL Server provides built-in functions to efficiently handle such calculations.

Built-In Function

In SQL Server 2012 and later versions, the EOMONTH function offers a direct solution:

SELECT DAY(EOMONTH(@ADate)) AS DaysInMonth

Where @ADate is the given date for which you want to determine the number of days in the month. EOMONTH returns the last day of the month, and DAY extracts the day number from that result, effectively providing the desired number of days in the month.

User-Defined Function

Prior to SQL Server 2012, a user-defined function can be created to achieve this functionality. Here's an example:

CREATE FUNCTION DaysInMonth(@ADate DATE)
RETURNS INT
BEGIN
    RETURN DATEDIFF(d, 1, DATEADD(m, 1, @ADate)) + 1
END

This function uses the DATEDIFF function to calculate the difference between the first day of the next month and the given date. Adding 1 to the result accounts for the last day of the current month.

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