DATEADD (Transact-SQL)
This function adds a specified number value (as a signed integer) to a specified datepart of an input date value, and then returns that modified value.
See Date and Time Data Types and Functions (Transact-SQL) for an overview of all Transact-SQL date and time data types and functions.
DATEADD (datepart , number , date )
datepart
The part of date to which DATEADD adds an integer number. This table lists all valid datepart arguments.
day的缩写是dd或d