dateadd is a T-SQL function that returns a datetime with the specified number interval added to a specified datepart of that datetime.
dateadd(datepart,number_of_units,date_time_value) is a T-SQL function available in MS SQL Server and the SAP/Sybase family of database products that can add and subtract from datetime values. Subtraction is accomplished by using a negative number_of_units value.
datepart is usually a two letter code which specifies which date or time segment is being added
number of units is a signed int value that specifies how much to add to the datepart
date_time_value is the datetime that is being manipulated.
