Oracle 11g Release 2

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CREATE TABLE TX(
C1 number(10),
C2 varchar2(50),
C3 varchar2(50));
INSERT INTO TX (C1,C2,C3)
VALUES (1,'A12','A');
1 rows affected

INSERT INTO TX (C1,C2,C3)
VALUES (2,'A12','A');
1 rows affected

INSERT INTO TX (C1,C2,C3)
VALUES (3,'A12','B');
1 rows affected

INSERT INTO TX (C1,C2,C3)
VALUES (4,'A12','A');
1 rows affected

INSERT INTO TX (C1,C2,C3)
VALUES (5,'A12','A');
1 rows affected

INSERT INTO TX (C1,C2,C3)
VALUES (6,'B11','B');
1 rows affected

INSERT INTO TX (C1,C2,C3)
VALUES (7,'B11','B');
1 rows affected

SELECT M.C1,M.C2,M.C3,1+SUM(M.Y) OVER (ORDER BY M.C1) AS D
FROM (
SELECT TX.*,
CASE WHEN C2=LAG(C2,1,C2) OVER (ORDER BY C1) AND C3=LAG(C3,1,C3) OVER (ORDER BY C1) THEN 0 ELSE 1 END AS Y
FROM TX) M
ORDER BY M.C1


C1
C2
C3
D


1
A12
A
1

2
A12
A
1

3
A12
B
2

4
A12
A
3

5
A12
A
3

6
B11
B
4

7
B11
B
4