SQL & PL/SQL

Hello,

I have the following table :

CREATE TABLE A_TEST (A INTEGER, B INTEGER, C INTEGER, D INTEGER, FLAG CHAR(11));

INSERT INTO A_TEST (A,B,C,D) VALUES(1,2,3,4);
INSERT INTO A_TEST (A,B,C,D) VALUES(2,4,5,8);
INSERT INTO A_TEST (A,B,C,D) VALUES(1,2,3,4);
INSERT INTO A_TEST (A,B,C,D) VALUES(2,4,5,8);
INSERT INTO A_TEST (A,B,C,D) VALUES(7,2,3,4);
INSERT INTO A_TEST (A,B,C,D) VALUES(9,2,3,4);
INSERT INTO A_TEST (A,B,C,D) VALUES(7,2,3,4);
INSERT INTO A_TEST (A,B,C,D) VALUES(1,2,3,4);
INSERT INTO A_TEST (A,B,C,D) VALUES(5,4,5,8);
INSERT INTO A_TEST (A,B,C,D) VALUES(2,2,3,9);
INSERT INTO A_TEST (A,B,C,D) VALUES(2,4,5,8);
INSERT INTO A_TEST (A,B,C,D) VALUES(6,2,3,4);
INSERT INTO A_TEST (A,B,C,D) VALUES(1,3,3,4);
INSERT INTO A_TEST (A,B,C,D) VALUES(8,2,8,4);


I would like to perform an update on the FLAG column by setting to "D" if it is a duplicate record.1,2,3,4);


I would like to use the rank function.

Desired update:

A B C D FLAG
1 2 3 4
2 4 5 8
1 2 3 4 D
2 4 5 8 D
7 2 3 4
9 2 3 4
7 2 3 4 D
1 2 3 4 D
5 4 5 8
2 2 3 9
2 4 5 8
6 2 3 4
1 3 3 4
8 2 8 4


Thank you