Virtual Date Column as paritition doesn't work

SQL> create table t ( 2 REF_NO VARCHAR2(100) , 3 REF_DATE DATE GENERATED ALWAYS AS (CASE 4 WHEN REF_NO LIKE 'XX%' 5 THEN TRUNC(TO_DATE(SUBSTR(REF_NO,3,2),'YY'),'YEAR')+(TO_NUMBER(SUBSTR(REF_NO,5,3))-1) 6 ELSE TRUNC(TO_DATE(SUBSTR(REF_NO,4,2),'YY'),'YEAR ...