Само за да избегна двойна работа, ето данните (замених включващия горен граничен отсек с изключителен, който е по-често срещан, IMHO):
-- CREATE SCHEMA tmp;
DROP TABLE tmp.gaps CASCADE;
CREATE TABLE tmp.gaps
( id INTEGER NOT NULL PRIMARY KEY -- surrogate key
, ztype CHAR(1) NOT NULL
, start_datetime TIMESTAMP NOT NULL -- lower boundary := inclusive
, end_datetime TIMESTAMP NOT NULL -- upper boundary := exclusive
);
CREATE UNIQUE INDEX gaps_forward ON tmp.gaps(ztype,start_datetime);
CREATE UNIQUE INDEX gaps_backward ON tmp.gaps(ztype,end_datetime);
INSERT INTO tmp.gaps(id,ztype,start_datetime,end_datetime) VALUES
(1,'a', '2012-01-11 00:00:00', '2012-01-15 00:00:00' )
,(2,'a', '2012-01-18 00:00:00', '2012-01-21 00:00:00' )
,(3,'b', '2012-01-14 00:00:00', '2012-01-20 00:00:00' )
,(4,'c', '2012-01-10 00:00:00', '2012-01-16 00:00:00' )
,(5,'d', '2012-01-11 00:00:00', '2012-01-21 00:00:00' )
,(6,'e', '2012-01-11 00:00:00', '2012-01-15 00:00:00' ) -- added this
,(7,'e', '2012-01-15 00:00:00', '2012-01-21 00:00:00' ) -- and this
;
-- SELECT * FROM tmp.gaps;
АКТУАЛИЗАЦИЯ:тук идва CTE. В първия UNION добавям два фалшиви интервала отляво и отдясно на желания (12 януари -- 19 януари) интервал.
За ztype преброявам общия брой интервали. Това трябва да е една, ако няма дупки, две, ако има една дупка и т.н. Това също така ще намери пропуски за ztype, които нямат никакви записи в желания интервал.
-- EXPLAIN ANALYZE
WITH RECURSIVE meuk(ztype,start_datetime,end_datetime) AS (
-- For every possible "ztype" add two dummie records
-- just before and just after our wanted interval.
WITH plus2 AS (
SELECT g0.ztype,g0.start_datetime,g0.end_datetime FROM tmp.gaps g0
WHERE (g0.start_datetime <= '2012-01-12 00:00:00' AND g0.end_datetime >= '2012-01-12 00:00:00')
OR (g0.start_datetime >= '2012-01-12 00:00:00' AND g0.end_datetime <= '2012-01-19 00:00:00')
OR (g0.start_datetime <= '2012-01-19 00:00:00' AND g0.end_datetime >= '2012-01-19 00:00:00')
UNION ALL SELECT DISTINCT g1.ztype, '1900-01-01 00:00:00'::timestamp, '2012-01-12 00:00:00'::timestamp FROM tmp.gaps g1
UNION ALL SELECT DISTINCT g2.ztype, '2012-01-19 00:00:00'::timestamp, '2100-01-01 00:00:00'::timestamp FROM tmp.gaps g2
)
SELECT p0.ztype,p0.start_datetime,p0.end_datetime
FROM plus2 p0
-- the start of a stretch: there is no older overlapping
-- (or touching) interval
WHERE NOT EXISTS (SELECT *
FROM plus2 nx
WHERE nx.ztype = p0.ztype
AND nx.start_datetime < p0.start_datetime -- older
AND nx.end_datetime >= p0.start_datetime -- touching or overlapping
)
UNION
SELECT mk.ztype
, LEAST(mk.start_datetime,p1.start_datetime)
, GREATEST(mk.end_datetime,p1.end_datetime)
FROM plus2 p1
, meuk mk
WHERE p1.ztype = mk.ztype
AND (p1.start_datetime >= mk.start_datetime AND p1.start_datetime <= mk.end_datetime AND p1.end_datetime > mk.end_datetime)
)
SELECT ztype, COUNT(*)-1 AS ngap
FROM meuk mk
WHERE NOT EXISTS (SELECT *
FROM meuk nx
WHERE nx.ztype = mk.ztype
AND (nx.start_datetime,nx.end_datetime) OVERLAPS( mk.start_datetime,mk.end_datetime)
AND (nx.end_datetime - nx.start_datetime) > (mk.end_datetime - mk.start_datetime)
)
GROUP BY ztype
ORDER BY ztype
;
Създаването на крайната сума е оставено като упражнение за читателя;-)
РЕЗУЛТАТИ:
ztype | ngap
-------+------
a | 1
b | 1
c | 1
d | 0
e | 0
(5 rows)