Another gap detection - mysql

Question

Have looked through many examples, but i have not found a good answer for my specific situation.
Basically, I have table with an unique ID and a sequence for each ID.
I want to detect gaps in the sequence for each ID.
I managed to do it using a query, but the query takes the exact ID in the where clause, and given the number of rows in my table, this is not wanted.
CREATE TABLE `t` (
`target_id` varchar(100) NOT NULL,
`version` int(11) NOT NULL,
PRIMARY KEY (`target_id`,`version`)
);
insert into t values
('abc',1),
('abc',2),
('abc',3),
('abc',4),
('abc',5),
('abc',6),
('abc',7),
('abc',8),
('xyz',1),
('xyz',2),
('xyz',3),
('xyz',5),
('xyz',6);
http://sqlfiddle.com/#!9/8c280a/7
I tried with something like
select distinct target_id as target, gap_ends_at,gap_starts_at from
category_event e inner join
(
SELECT target_id as x, (t1.version + 1) as gap_starts_at,
(SELECT MIN(t3.version) -1 FROM category_event t3 WHERE t3.version >
t1.version and target_id=e.target) as gap_ends_at
FROM category_event t1
WHERE NOT EXISTS (SELECT t2.version FROM category_event t2 WHERE t2.version = t1.version + 1 and target_id=e.target) and target_id=e.target
HAVING gap_ends_at IS NOT NULL
) as x;
But that fails.
I expect a resultset like
id, gap_starts_at, gap_ends_at

Answer 1

Because this is MySQL, you can solve it just using vars:
MySQL 5.6 Schema Setup:
CREATE TABLE `t` (
`target_id` varchar(100) NOT NULL,
`version` int(11) NOT NULL,
PRIMARY KEY (`target_id`,`version`)
);
insert into t values
('abc',1),
('abc',2),
('abc',3),
('abc',4),
('abc',5),
('abc',6),
('abc',7),
('abc',8),
('xyz',1),
('xyz',2),
('xyz',3),
('xyz',5),
('xyz',6)
Query 1:
select
gap
from (
Select
target_id,
#v := case when #t <> target_id then 1 else #v+1 end,
#t := case when #t <> target_id then target_id else #t end,
case when #v <> version then CONCAT_WS(' ' ,
'gap for ',
target_id,
' start at',
CAST(#v-1 as CHAR(50)) ,
'ends at ',
CAST(version as CHAR(50))
)
else null end as gap,
#v := version
from
(select target_id, version
from t
order by target_id, version ) S,
( select #t:='', #v=0 ) I
) X
where gap > ''
Results:
| gap |
|-------------------------------------|
| gap for xyz start at 3 ends at 5 |