UNSET
Unsets the currently set value of a parameter.
Syntax
UNSET [SESSION|GLOBAL] parameter-name | ALL
Description
The value can be unset at either the session or the global level. Unset can only be used over a parameter whose values are set at the same level, namely: a global-level Unset can only be applied to a global-level parameter. If unset level is not specified, session level is assumed.