Converting BLOB column data type to CLOB is a very tedious task, since you cannot do it directly.

 

First, you need to create an “Oracle Function” under an oracle schema you have access to, the following is the function:

 

CREATE OR REPLACE FUNCTION blob_to_clob (blob_in IN BLOB)

RETURN CLOB

AS

v_clob CLOB;

v_varchar VARCHAR2(32767);

v_start PLS_INTEGER := 1;

v_buffer PLS_INTEGER := 32767;

BEGIN

DBMS_LOB.CREATETEMPORARY(v_clob, TRUE);

 

FOR i IN 1..CEIL(DBMS_LOB.GETLENGTH(blob_in) / v_buffer)

LOOP

 

v_varchar := UTL_RAW.CAST_TO_VARCHAR2(DBMS_LOB.SUBSTR(blob_in, v_buffer, v_start));

 

DBMS_LOB.WRITEAPPEND(v_clob, LENGTH(v_varchar), v_varchar);

v_start := v_start + v_buffer;

END LOOP;

RETURN v_clob;

END blob_to_clob;

/

 

Second, alter the table by adding a temporary column with a name similar to the BLOB column name.

For example, let’s say the BLOB column name is STRING_NAMES, the new CLOB column will be STRING_NAMES2

 

Sql command:

 

Alter table DUMMY.TABLE add (STRING_NAMES2 CLOB);

 

Then, use the “update” statement to populate the column with the converted data:

 

update DUMMY.TABLE  set STRING_NAMES2=blob_to_clob(STRING_NAMES);

 

Once finished drop the original column, then rename the new one to the original name.

 

If your table has huge number of records, you may need to develop a script and schedule it to perform this intensive information.

*** UPDATE:

another way of converting BLOB to CLOB can be found here:

https://geodatamaster.wordpress.com/2014/01/01/convert-blob-to-clob-column-method-2/