oracle drop job if exists
DECLARE
l_job_exists NUMBER;
BEGIN
SELECT count(*) INTO l_job_exists FROM ALL_SCHEDULER_JOBS
WHERE JOB_NAME = 'job_name' AND OWNER = 'owner_name';
IF l_job_exists = 1 THEN
dbms_scheduler.drop_job(job_name => 'STATISTICS_COLUMNS_JOB');
END IF;
END;