database - Oracle: Changing VARCHAR2 column to CLOB

Question

I have an encountered an issue where the data I was trying to store in my varchar2(4000) column was too big, so I wish to change the column to one more suitable for storing large amounts of textual data. Specifically, a serialized array.

1. Firstly, is CLOB the best data type for me to use for this purpose? Is there a more appropriate data type?

2. Secondly, when I try to alter the column using the usual snyntax:

   ALTER TABLE table MODIFY column CLOB
   

   I get the following error: ORA-22858: invalid alteration of datatype

   What's the most straightforward way to alter this table without losing any data?

question from:https://stackoverflow.com/questions/13402510/oracle-changing-varchar2-column-to-clob

Answer 1

The most straightforward way, given that the operation of moving from a varchar column to a CLOB is disallowed, would be to create a new column and move the data from the old column to the new column:

ALTER TABLE some_table ADD (foo CLOB);
UPDATE some_table SET foo = old_column;
ALTER TABLE some_table DROP COLUMN old_column;
ALTER TABLE some_table RENAME COLUMN foo TO old_column;