Do you want to know if a function has already exists in sql server? This quick check if condition may come handy especially if you want to run a batch sql query.
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[my_function]') AND type IN ( N'FN', N'IF', N'TF', N'FS', N'FT' )) DROP FUNCTION [dbo].[my_function] GO