How to change column varchar to clob in oracle

Question

I have a column details designed as varchar in oracle DB, this DB is being used now for customers and some rows already have data stored.

Now I want to change the column details to a Clob column. What is a smart way to accomplish this？

Answer 1

(as the previous answer) and here's the code:

ALTER TABLE atable  ADD (tmpdetails  CLOB);  UPDATE atable SET tmpdetails=details; COMMIT;  ALTER TABLE atable DROP COLUMN details;  ALTER TABLE atable RENAME COLUMN tmpdetails TO details; 

Answer 2

1. Add a clob column to the table
2. update clob column with values from varchar column
3. drop varchar column
4. rename clob column to varchar columns name