Easily and efficiently? Well, not quite, but it is doable if your table is smallish (alternatively, you could write a stored procedure, execute block or possibly a recursive CTE.

SELECT cast('Empty' as CHAR(10)) as MyRange, t1.T as MinValue, t2.T as MaxValue
FROM T_10199000 t1
JOIN T_10199000 t2 on t1.D = t2.D
and t1.P = t2.P
and t1.V = t2.V
and t1.T < t2.T
LEFT JOIN T_10199000 tNot on t1.D = tNot.D
and t1.P = tNot.P
and t1.V = tNot.V
and t1.T < tNot.T
and t2.T > tNot.T
where tNot.D is NULL /*whatever your primary key is, the point is to ascertain such a row doesn't exist*/
and t2.T - t1.T > 1.000000 / 86400 /*You might have to tweak a bit, there are 86400 seconds in a day, but you might */
/*not want 10:11:15.0000 and 10:11:16.0002 to be considered a gap. */
union
SELECT 'Contiguous', t1.T as MinEmpty, t2.T as MaxEmpty
FROM T_10199000 t1
JOIN T_10199000 t2 on t1.D = t2.D
and t1.P = t2.P
and t1.V = t2.V
and t1.T < t2.T
LEFT JOIN T_10199000 tNot1 on t1.D = tNot1.D
and t1.P = tNot1.P
and t1.V = tNot1.V
and t1.T > tNot1.T
and t1.T between tNot1.T and tNot1.T + (1.000000 / 86400) /*Just before*/
LEFT JOIN T_10199000 tNot2 on t2.D = tNot2.D
and t2.P = tNot2.P
and t2.V = tNot2.V
and t2.T < tNot2.T
and t2.T between tNot2.T - (1.000000 / 86400) and tNot2.T /*Just after*/
where tNot1.D is NULL /*None just before*/
and tNot2.D is NULL /*None just after*/
and t2.T - t1.T < 1.000000 / 86400

HTH,
Set

-----Original Message-----
From: firebird-support@yahoogroups.com [mailto:firebird-support@yahoogroups.com] On Behalf Of ehaerim
Sent: 19. mai 2011 06:43
To: firebird-support@yahoogroups.com
Subject: [firebird-support] How to select contiguous and empty ranges?

A table is created using

CREATE TABLE T_10199000(D DATE NOT NULL, T TIME NOT NULL, P DOUBLE PRECISION NOT NULL, V FLOAT NOT NULL, PRIMARY KEY (D, T), CHECK(V >= 0));

Given a search range, (FromDate, FromTime) and (ToDate, ToTime),

[1] I would like to find out all the ranges each of which is either contiguous or empty. Here "contiguous" means the seconds values are in a row in ascending order without any gap. "Empty" means literally a vacant range without any data.

(ex)
Following 7 records were inserted into the table.
INSERT INTO T_10199000(D, T, P, V) VALUES('2011-05-13', '10:11:11.0000', 280.85, 25.0);
INSERT INTO T_10199000(D, T, P, V) VALUES('2011-05-13', '10:11:12.0000', 280.85, 25.0);
INSERT INTO T_10199000(D, T, P, V) VALUES('2011-05-13', '10:11:12.0001', 280.85, 25.0);
INSERT INTO T_10199000(D, T, P, V) VALUES('2011-05-13', '10:11:15.0000', 280.85, 25.0);
INSERT INTO T_10199000(D, T, P, V) VALUES('2011-05-13', '10:11:15.0001', 280.85, 25.0);
INSERT INTO T_10199000(D, T, P, V) VALUES('2011-05-13', '10:11:18.0000', 280.85, 25.0);
INSERT INTO T_10199000(D, T, P, V) VALUES('2011-05-13', '10:11:18.0001', 280.85, 25.0);

In this example,
- 3 contiguous ranges :
-- from (2011-05-13, 10:11:11) to
(2011-05-13, 10:11:12)
-- from (2011-05-13, 10:11:15) to
(2011-05-13, 10:11:15)
-- from (2011-05-13, 10:11:18) to
(2011-05-13, 10:11:18)

- 2 empty ranges:
-- from (2011-05-13, 10:11:13) to
(2011-05-13, 10:11:14)
-- from (2011-05-13, 10:11:16) to
(2011-05-13, 10:11:17)


[2] Next, for each range,
if it is a contiguous range, I would retrieve all the records belonging to that range.
if it is an empty range, I would do request data for that emtpy range from external data source and insert them into that missing range.

[3] Finally, after iterating all the ranges, the table T_10199000 will have no empty range left.


I guess Firebird SQL could do this and maybe quite easily and efficiently.

Can someone please write SQL code for the above job?

Thanks a lot.

HaeRim