Je vhodnější použít virtuální sloupce
create table t2( col_name varchar2(10) );
insert into t2(col_name) values('hsaJDadkD');
ALTER TABLE t2 ADD (col_name2 GENERATED ALWAYS AS (SUBSTR(col_name,-3))); --virtual column
Select * from T2;
COL_NAME COL_NAME
---------- --------
hsaJDadkD dkD