How to drop Default Constraint on a Table Column without knowing the Constraint Name for MS SQL Server 2005

ALTER PROC SP_DROP_Default_Constraint 
(
	@table_name sysname, 
	@column_name sysname
)
AS

--declare @table_name sysname, @column_name sysname, 
declare @default_constraint_name sysname, @sql nvarchar(max)
--select @table_name = N'SampleConstraintsSQLTable', @column_name = N'IsDefaultConstraintColumn'

if exists (
	select * 
	from sys.default_constraints 
	where 
		parent_object_id = OBJECT_ID(@table_name)
		AND type = 'D'
		AND parent_column_id = (
			select column_id 
			from sys.columns 
			where 
			object_id = OBJECT_ID(@table_name)
			and name = @column_name
		)
)
begin
	select @default_constraint_name = name 
	from sys.default_constraints 
		where 
			parent_object_id = OBJECT_ID(@table_name)
			AND type = 'D'
			AND parent_column_id = (
				select column_id 
				from sys.columns 
				where 
				object_id = OBJECT_ID(@table_name)
				and name = @column_name
			)

	SET @sql = N'ALTER TABLE ' + @table_name + ' DROP Constraint ' + @default_constraint_name

	exec sp_executesql @sql
end

GO