Need help with calculating differences in row values using cursor

From: omar_mpls <omar_mpls_at_hotmail.com>
Date: 22 Aug 2006 17:06:51 -0700
Message-ID: <1156291611.464758.303260@74g2000cwt.googlegroups.com>

CREATE TABLE Error

     ( Serial_Num  VARCHAR2(10),
       Run_Hrs NUMBER(8) NOT NULL,
       Error_Cnt NUMBER(4)
     );

INSERT INTO Error VALUES('A', 10, 2);
INSERT INTO Error VALUES('B', 10, 5);
INSERT INTO Error VALUES('B', 20, 7);
INSERT INTO Error VALUES('B', 30, 7);
INSERT INTO Error VALUES('B', 40, 10);
INSERT INTO Error VALUES('C', 20, 3);

INSERT INTO Error VALUES('C', 50, 5);
INSERT INTO Error VALUES('C', 100, 5);

Select * from Error

SERIAL_NUM	 RUN_HRS		   ERROR_CNT
A				10			   2
B				10			   5
B				20			   7
B				30			   7
B				40			   10
C				20			   3
C				50			   5
C				100			   5

I would like to add the differences (new errors) for each row and each Serial_Num.
My goal is to create the following result set using cursor.

SERIAL_NUM	 RUN_HRS  ERROR_CNT 	   NEW_ERRORS
A				10	  2				   2
B				10	  5				   5
B				20	  7				   2
B				30	  7				   0
B				40	  10			   3
C				20	  3				   3
C				50	  5				   2
C				100	  5				   0

/******************************************

This is what I wrote to get the desired result set and obviuosly there are some
errors in there. Threfore I was not able to get the result set. If any one would
be kind enough to review my code and correct it so that I can get the desired result
set would be very much apprecited.

*******************************************/

SET SERVEROUTPUT ON; Declare

cur_serial_num  	  error.serial_num%TYPE := '';
cur_error_count  	  error.error_cnt%TYPE := 0;
new_errors 	  	  error.error_cnt%TYPE := 0;

BEGIN
FOR error_rec IN (select * from error order by serial_num, run_hrs) LOOP

	 IF error_rec.serial_num = cur_serial_num
	 	THEN
	 		 new_errors := (error_rec.error_cnt - cur_error_count);
	 	ELSE
	 	 	 new_errors := error_rec.error_cnt;
	  END IF;
	  cur_error_count := error_rec.error_cnt;
	  cur_serial_num :=  error_rec.serial_num;

DBMS_OUTPUT.PUT_LINE(error_rec.serial_num || '-' || error_rec.run_hrs || '-' || error_rec.error_cnt || '-' || new_errors ); END LOOP;
END; Received on Tue Aug 22 2006 - 19:06:51 CDT