Returns an integer representing the day (day of the month) of the specified date.
For an overview of all Transact-SQL date and time data types and functions, see Date and Time Functions (Transact-SQL). For information and examples that are common to date and time data types and functions, see Using Date and Time Data.
DAY returns the same value as DATEPART (day, date).
If date contains only a time part, the return value is 1, the base day.