Purpose: The Day() function returns an integer corresponding to the day of the month (1-31) corresponding to the input date.
The input date_expression is usually a string value or date invariant, but can be any expression that evaluates to a date in the range January 1, 100 through December 31, 9999.
Returns: Integer corresponding to the day of the month of date_expression.
Examples and Special Cases
Day(February 1, 2006) returns 1 Day(2/12/2006) returns 12