Resetting/Unsetting parameters in oracle database

You can reset  parameter to default. For example, you set parameter sid wrongly when you config db. Then you can reset it with this command.

SQL> alter system set fast_start_mttr_target=1200 scope=spfile sid='wrong_sid';
System altered.
-- You will see "wrong_sid.fast_start_mttr_target=1200" in pfile.

SQL> alter system reset fast_start_mttr_target scope=spfile sid='wrong_sid';
System altered.
-- Cleaned wrong parameter in parameter file.