Finding efficient overlapping records in an SQL table

Question

What is the most efficient way to find all records that overlap in the same table? Each entry has a start and end date. For example, I have the following database setup:

CREATE TABLE DEMO
(
    DEMO_ID  int  IDENTITY ,
    START date  NOT NULL ,
    END  date  NOT NULL
);

INSERT INTO DEMO (DEMO_ID, START, END) VALUES (1, '20100201', '20100205');
INSERT INTO DEMO (DEMO_ID, START, END) VALUES (2, '20100202', '20100204');
INSERT INTO DEMO (DEMO_ID, START, END) VALUES (3, '20100204', '20100208');
INSERT INTO DEMO (DEMO_ID, START, END) VALUES (4, '20100206', '20100211');

My request is as follows:

SELECT DISTINCT * 
FROM DEMO A, DEMO B
WHERE A.DEMO_ID != B.DEMO_ID
AND A.START < B.END
AND B.START < A.END

The problem is that in my demo table, for example, 20'000 rows, the request takes too much time. My MS SQL Server 2008 environment. Thanks for a more efficient solution.

Answer 1

It is simpler and runs in about 2 seconds for over 20,000 entries

select * from demo a
where not exists(
select 1 from demo b 
where a.demo_id!=b.demo_id
AND A.S < B.E
AND B.S < A.E)

Answer 2

You can rewrite the query a bit:

SELECT A.DEMO_ID, B.DEMO_ID 
FROM DEMO A, DEMO B
WHERE A.DEMO_ID != B.DEMO_ID
AND A.START >= B.START
AND A.START <= B.END

DISTINCT , Sql Server ( DISTINCT *) .

. Sql Server 2008 START, END, DEMO_ID.

Answer 3

:

Start End

DECLARE @t table (
    Position int identity(1,1),
    DEMO_ID  int,
    START date  NOT NULL ,
    END  date  NOT NULL
)
INSERT INTO @t (DEMO_ID, START, END)
    SELECT DEMO_ID, START, END
    FROM DEMO
    ORDER BY START, END

:

SELECT t.DEMO_ID
FROM @t t INNER JOIN @t u ON t.Position + 1 = u.Position
WHERE u.Start <= t.End
UNION
SELECT t.DEMO_ID
FROM @t t INNER JOIN @t u ON t.Position - 1 = u.Position
WHERE t.Start <= u.End

, , . , .

Answer 4

Late answer, but I wonder if this will help:

create index IXNCL_Demo_DemoId on Demo(Demo_Id)

select a.demo_id, b.demo_id as [CrossingDate]
from demo a
    cross join demo b
    where a.[end] between b.start and b.[end]
    and a.demo_id <> b.demo_id