sql finding gaps in a couple number/year - sql

Question

I have a table like:
id
number
year
I want to find "holes", or gaps, not considering the id but only the couple year/number.
There is a gap when, for the same year, there are two non-consecutive numbers, the result being the year and all the numbers between (excluding extremes) those two non-consecutive numbers. Also note that the lower end is always 1 so that if 1 is missing, it is a gap.
For example, having:
id n year
1 1 2012
2 2 2012
3 5 2012
4 2 2010
I want as a result:
3/2012
4/2012
1/2010

Answer 1

The trick to finding missing entries in sequences is to generate a cartesian product of all available combinations in the sequence, then use NOT EXISTS to elimate those that exist. This is hard to do in a non DBMS specific way because all have different ways in which to optmially create a sequence on the fly. For Oracle I use:
SELECT RowNum AS r
FROM Dual
CONNECT BY Level <= MaxRequiredValue;
So, to generate a list of all available year/n pairs I would use:
SELECT d.Year, n.r
FROM ( SELECT year, MAX(n) AS MaxN
FROM T
GROUP BY Year
) d
INNER JOIN
( SELECT RowNum AS r
FROM Dual
CONNECT BY Level <= (SELECT MAX(n) FROM T)
) n
ON r < MaxN;
Where I am getting the Maximum n for each year and joining this to a list of integers from 1 to the highest n of all where this integer lists highest value is less than that years maximium value.
Finally use NOT EXISTS to elimate the values that already exist:
SELECT d.Year, n.r
FROM ( SELECT year, MAX(n) AS MaxN
FROM T
GROUP BY Year
) d
INNER JOIN
( SELECT RowNum AS r
FROM Dual
CONNECT BY Level < (SELECT MAX(n) FROM T)
) n
ON r = MaxN
WHERE NOT EXISTS
( SELECT 1
FROM T
WHERE d.Year = t.Year
AND n.r = t.n
);
Working example on SQL Fiddle
EDIT
Since I couldn't find a non DMBS specific solution I thought I'd better do the decent thing and create some examples for other DBMS.
SQL Server Example
Postgresql Example
My SQL Example

Answer 2

Another option is to use a temporary table like so:
create table #tempTable ([year] int, n int)
insert
into #tempTable
select t.year, 1
from tableName t
group by t.year
while exists(
select *
from tableName t1
where t1.n > (select MAX(t2.n) from #tempTable t2 where t2.year = t1.year)
)
begin
insert
into #tempTable
select t1.year,
(select MAX(t2.n)+1 from #tempTable t2 where t2.year = t1.year)
from tableName t1
where t1.n > (select MAX(t2.n) from #tempTable t2 where t2.year = t1.year)
end
delete t2
from #tempTable t2
inner join tableName t1
on t1.year = t2.year
and t1.n = t2.n
select [year], n
from #tempTable
drop table #tempTable