Data Dump and Exceptions

Question

After reading docs on Data Pump Open call (dbms_datapump.open), it looks like the exception JOB_EXISTS is a predefined but I can't get my code to recognize it. Do I need to declare something? Any ideas?
declare
my_handle number;
my_db_link varchar2(500) := 'DWREDEVLINK' ;
my_job_name varchar2 (500) := 'LISTING_21';
begin
begin
my_handle := dbms_datapump.open (operation => 'IMPORT',
job_mode => 'TABLE',
remote_link => my_db_link,
job_name => my_job_name ,
version=>'LATEST' ) ;
exception
when JOB_EXISTS then
my_handle := dbms_datapump.attach(job_name => 'LISTING_21');
end;
end;
ERROR at line 16:
ORA-06550: line 16, column 8:
PLS-00201: identifier 'JOB_EXISTS' must be declared
ORA-06550: line 9, column 1:

Answer 1

select dump(column_name) from table_name;