Oracle query using Window function - oracle

Question

Please suppose I have an Oracle table called MYDATA, with the following content:
NAME, D1, D2
A, 01/01/2010, 02/03/2010
B, 03/03/2010, 20/03/2010
C, 10/03/2010, 20/09/2010
D, 10/12/2010, 31/12/2010
Insert into MYDATA
(NAME, D1, D2)
Values
('A', TO_DATE('01/01/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('03/02/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'));
Insert into MYDATA
(NAME, D1, D2)
Values
('B', TO_DATE('03/03/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('03/20/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'));
Insert into MYDATA
(NAME, D1, D2)
Values
('C', TO_DATE('03/10/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('09/20/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'));
Insert into MYDATA
(NAME, D1, D2)
Values
('D', TO_DATE('12/10/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('12/31/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'));
COMMIT;
I would like to mark with 'S' the records which have overlapping intervals: in this case, record B and record C overlap.
I have written the following Oracle query:
SELECT name, D1, D2, WMSYS.WM_CONCAT (OVERLAPPING)
FROM (SELECT T1.name, T1.D1, T1.D2, NULL OVERLAPPING
FROM MYDATA T1, MYDATA T2
WHERE NOT ( (T1.D1, T1.D2) OVERLAPS (T2.D1, T2.D2))
AND T1.NAME <> T2.NAME
UNION
SELECT T1.name, T1.D1, T1.D2, 'S'
FROM MYDATA T1, MYDATA T2
WHERE ( (T1.D1, T1.D2) OVERLAPS (T2.D1, T2.D2))
AND T1.NAME <> T2.NAME)
GROUP BY NAME, D1, D2;
The result is:
NAME, D1, D2, WMSYS.WM_CONCAT(OVERLAPPING)
A, 01/01/2010, 02/03/2010, NULL
B, 03/03/2010, 20/03/2010, S
C, 10/03/2010, 20/09/2010, S
D, 10/12/2010, 31/12/2010, NULL
As you can see, the table MYDATA joins itself, marking with 'S' the record which overlap.
I know that when a table joins itself, the corresponding query could be rewritten using Oracle windows functions.
At the end, the query to rewrite using Oracle Window Functions is the following:
SELECT NAME,
D1,
D2
FROM (SELECT T1.NAME,
T1.D1,
T1.D2
FROM MYDATA T1, MYDATA T2
WHERE ( (T1.D1, T1.D2) OVERLAPS (T2.D1, T2.D2))
AND T1.NAME <> T2.NAME)
GROUP BY NAME, D1, D2;
Could you me please help to rewrite the query avoiding the self join?
Thank you very much for considering my request.

Answer 1

You can use case with lead and lag:
SELECT D.*,
CASE
WHEN LAG (D1) OVER (ORDER BY D1) IS NOT NULL
AND (LAG (D1) OVER (ORDER BY D1), LAG (D2) OVER (ORDER BY D1))
OVERLAPS (D1, D2)
OR LEAD (D1) OVER (ORDER BY D1) IS NOT NULL
AND (LEAD (D1) OVER (ORDER BY D1),
LEAD (D2) OVER (ORDER BY D1))
OVERLAPS (D1, D2)
THEN
'S'
ELSE
'N'
END
OVERLAP
FROM MYDATA D;
Results:
NAME D1 D2 OVERLAP
-------------------------------------------------- --------- --------- -------
A 01-JAN-10 02-MAR-10 N
B 03-MAR-10 20-MAR-10 S
C 10-MAR-10 20-SEP-10 S
D 10-DEC-10 31-DEC-10 N