DROP FUNCTION (Transact-SQL)
DROP FUNCTION will fail if there are Transact-SQL functions or views in the database that reference this function and were created by using SCHEMABINDING, or if there are computed columns, CHECK constraints, or DEFAULT constraints that reference the function.
DROP FUNCTION will fail if there are computed columns that reference this function and have been indexed.
A. Dropping a function
The following example drops the fn_SalesByStore user-defined function from the Sales schema in the AdventureWorks2008R2 sample database. To create this function, see Example B in CREATE FUNCTION (Transact-SQL).