create table stage_complaint(
    complaint_key integer,
    complaint_id integer,
    cancellation_reason varchar(255),
    complaint_status varchar(255),
    complaint_type varchar(255),
    compentation_status varchar(255)
);

ALTER TABLE stage_complaint ADD CONSTRAINT stg_complaint_pk PRIMARY KEY (complaint_key);

desc stage_complaint;

DESC complaint;

CREATE SEQUENCE Complaint_seq
START WITH 1
INCREMENT BY 1
MAXVALUE 99999999
MINVALUE 1
NOCYCLE;

UPDATE stage_complaint SET complaint_key = Complaint_seq.NEXTVAL;

CREATE TRIGGER Complaint_trigger
  BEFORE INSERT ON stage_complaint
  FOR EACH ROW
BEGIN
  SELECT Complaint_seq.nextval
    INTO :new.complaint_key
    FROM dual;
END;

MERGE INTO stage_complaint SC
USING (SELECT complaint_id,description,complaint_status,complaint_type,compensation_amnt FROM complaint) C
ON (
    SC.complaint_id = C.complaint_id
)
WHEN MATCHED THEN
UPDATE SET
    SC.cancellation_reason = C.description,
    SC.complaint_status = C.complaint_status,
    SC.complaint_type = C.complaint_type,
    SC.compentation_status = C.compensation_amnt
WHEN NOT MATCHED THEN
INSERT VALUES (Complaint_seq.NEXTVAL,C.complaint_id, C.description, C.complaint_status,C.complaint_type,C.compensation_amnt);

select * from stage_complaint