如何把varchar2類型的字段切換成clob

具體操作如下：

原字段bookdetails是varchar2(4000),原表已經有業務數據

ALTER TABLE test
ADD (bookdetails01 CLOB);

UPDATE test SET bookdetails01=bookdetails;
COMMIT;

ALTER TABLE test DROP COLUMN bookdetails;

ALTER TABLE atable
RENAME COLUMN bookdetails01 TO bookdetails;