Both are predefined functions available in SqlServer 2005 on wards. They are generally use to fetch part of date. For instance "08/13/2015" we want to fetch year only.Datepart() returns value as Integer. But Datename() returns value as string characters. So you can't do any operation like add 1 year to result in case of Datename() but you can do with Datepart().More on this please visit: http://www.c-sharpcorner.com/Blogs/49779/difference-between-datename-and-datepart-in-sql-server.aspx

Both are almost same but in case of return value datepart returns INTEGER where datename returns stringie. datepart(month,getdate()) = 1 datename(month,getdate()) = january

detepart() gives the particular section(eg: year or month) in a date and datename function returns name of the particular datepart.. datepart(month,"12/05/1990")->gives 05; datename(month,"12/05/1990")->gives may;

Both are almost same but in case of return value datepart returns INTEGER where datename returns string