Exporting a CLOB to a text file using Oracle SQL Developer

if you have access to the file system on your database box you could do something like this:

CREATE OR REPLACE DIRECTORY documents AS 'C:\';
SET SERVEROUTPUT ON
DECLARE
  l_file    UTL_FILE.FILE_TYPE;
  l_clob    CLOB;
  l_buffer  VARCHAR2(32767);
  l_amount  BINARY_INTEGER := 32767;
  l_pos     INTEGER := 1;
BEGIN
  SELECT col1
  INTO   l_clob
  FROM   tab1
  WHERE  rownum = 1;

  l_file := UTL_FILE.fopen('DOCUMENTS', 'Sample2.txt', 'w', 32767);

  LOOP
    DBMS_LOB.read (l_clob, l_amount, l_pos, l_buffer);
    UTL_FILE.put(l_file, l_buffer);
    l_pos := l_pos + l_amount;
  END LOOP;
EXCEPTION
  WHEN OTHERS THEN
    DBMS_OUTPUT.put_line(SQLERRM);
    UTL_FILE.fclose(l_file);
END;
/

Which I copied and pasted from this site.

You may also find this previous question about UTL_FILE useful. It addresses exporting to CSV. I have no idea or experience with how UTL_FILE handles CLOBs, however.

You can use a Python script to take care of the export, the CLOBs won't get truncated:

from __future__ import print_function
from __future__ import division

import time
import cx_Oracle

def get_cursor():
    '''
    Get a cursor to the database
    '''
    # https://stackoverflow.com/questions/24149138/cx-oracle-doesnt-connect-when-using-sid-instead-of-service-name-on-connection-s
    # http://www.oracle.com/technetwork/articles/dsl/prez-python-queries-101587.html
    ip = '' # E.g. '127.0.0.1'
    port = '' # e.g. '3306'
    sid = ''
    dsnStr = cx_Oracle.makedsn(ip, port, sid)
    username = '' # E.g. 'FRANCK'
    password = '' # E.g. '123456'
    db = cx_Oracle.connect(user=username, password=password, dsn=dsnStr)    
    cursor = db.cursor()
    return cursor

def read_sql(filename):
    '''
    Read an SQL file and return it as a string
    '''
    file = open(filename, 'r')
    return ' '.join(file.readlines()).replace(';', '')

def execute_sql_file(filename, cursor, verbose = False, display_query = False):
    '''
    Execute an SQL file and return the results
    '''
    sql = read_sql(filename)
    if display_query: print(sql)
    start = time.time()
    if verbose: print('SQL query started... ', end='')
    cursor.execute(sql)
    if verbose: 
        end = time.time()
        print('SQL query done. (took {0} seconds)'.format(end - start))
    return cursor


def main():
    '''
    This is the main function
    '''
    # Demo:
    cursor = get_cursor()
    sql_filename = 'your_query.sql' # Write your query there
    cursor = execute_sql_file(sql_filename, cursor, True)    
    result_filename = 'result.csv'   # Will export your query result there
    result_file = open(result_filename, 'w')
    delimiter = ','    
    for row in cursor:
        for count, column in enumerate(row):
            if count > 0: result_file.write(delimiter)
            result_file.write(str(column))
        result_file.write('\n')
    result_file.close()


if __name__ == "__main__":
    main()
    #cProfile.run('main()') # if you want to do some profiling

FYI: Help installing cx_Oracle