How to find “holes” in a table

Question

I recently inherited a database on which one of the tables has the primary key composed of encoded values (Part1*1000 + Part2).
I normalized that column, but I cannot ch

Answer 1

This solution doesn't give all holes in table, only next free ones + first available max number on table - works if you want to fill in gaps in id-es, + get free id number if you don't have a gap..

select numb + 1 from temp minus select numb from temp;

Answer 2

This solution should give you the first and last ID values of the "holes" you are seeking. I use this in Firebird 1.5 on a table of 500K records, and although it does take a little while, it gives me what I want.

SELECT l.id + 1 start_id, MIN(fr.id) - 1 stop_id
FROM (table l
LEFT JOIN table r
ON l.id = r.id - 1)
LEFT JOIN table fr
ON l.id < fr.id
WHERE r.id IS NULL AND fr.id IS NOT NULL
GROUP BY l.id, r.id

For example, if your data looks like this:

ID
1001
1002
1005
1006
1007
1009
1011

You would receive this:

start_id   stop_id
1003       1004
1008       1008
1010       1010

I wish I could take full credit for this solution, but I found it at Xaprb.

Answer 3

Many of the previous answer are quite good. However they all miss to return the first value of the sequence and/or miss to consider the lower limit 100000. They all returns intermediate holes but not the very first one (100001 if missing).

A full solution to the question is the following one:

select id + 1 as newid from
    (select 100000 as id union select id from tbl) t
    where (id + 1 not in (select id from tbl)) and
          (id >= 100000)
    order by id
    limit 1;

The number 100000 is to be used if the first number of the sequence is 100001 (as in the original question); otherwise it is to be modified accordingly "limit 1" is used in order to have just the first available number instead of the full sequence

Answer 4

select ID +1 From Table t1
where not exists (select * from Table t2 where t1.id +1 = t2.id);

not sure if this version would be faster than the one you mentioned originally.