CREATE PROCEDURE [dbo].[dynamic_example]
  @lastname varchar(50) = NULL,
  @firstname varchar(50) = NULL
AS
BEGIN
  IF (@lastname IS NULL)
    IF (@firstname IS NULL)
      SELECT * from Users
    ELSE
      SELECT * from Users
       WHERE (users.firstname LIKE @firstname)
  ELSE
    IF (@firstname IS NULL)
      SELECT * from Users
       WHERE (users.lastname LIKE @lastname)
    ELSE
      SELECT * from Users
       WHERE (users.lastname LIKE @lastname)
         AND (users.firstname LIKE @firstname)
END
GO