Yea,,,,,
I doesn't work with PL/SQL?????? Why...?

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SQL> create or replace FUNCTION test101 RETURN timestamp IS
2 v timestamp;
3 BEGIN
4 select cast(systimestamp as time) into v from dual;
5 END;
6 /

Warning: Function created with compilation errors.

SQL> show err
Errors for FUNCTION TEST101:

LINE/COL ERROR
-------- -----------------------------------------------------------------
4/3 PL/SQL: SQL Statement ignored
4/10 PL/SQL: ORA-00932: inconsistent datatypes: expected NUMBER got
TIME

SQL> ******************************************************************

It's paradox...