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 will give you the complete picture, where 'Bottom' stands for gap start and 'Top' stands for gap end:

    select *
    from 
    ( 
       (select <COL>+1 as id, 'Bottom' AS 'Pos' from <TABLENAME> /*where <CONDITION*/>
       except
       select <COL>, 'Bottom' AS 'Pos' from <TABLENAME> /*where <CONDITION>*/)
    union
       (select <COL>-1 as id, 'Top' AS 'Pos' from <TABLENAME> /*where <CONDITION>*/
       except
       select <COL>, 'Top' AS 'Pos' from <TABLENAME> /*where <CONDITION>*/)
    ) t
    order by t.id, t.Pos

Note: First and Last results are WRONG and should not be regarded, but taking them out would make this query a lot more complicated, so this will do for now.

Answer 2

SELECT (ID+1) FROM table AS t1
LEFT JOIN table as t2
ON t1.ID+1 = t2.ID
WHERE t2.ID IS NULL

Answer 3

For people using Oracle, the following can be used:

select a, b from (
  select ID + 1 a, max(ID) over (order by ID rows between current row and 1 following) - 1 b from MY_TABLE
) where a <= b order by a desc;

Answer 4

The best way is building a temp table with all IDs

Than make a left join.

declare @maxId int
select @maxId = max(YOUR_COLUMN_ID) from YOUR_TABLE_HERE


declare @t table (id int)

declare @i int
set @i = 1

while @i <= @maxId
begin
    insert into @t values (@i)
    set @i = @i +1
end

select t.id
from @t t
left join YOUR_TABLE_HERE x on x.YOUR_COLUMN_ID = t.id
where x.YOUR_COLUMN_ID is null

Answer 5

Have thought about this question recently, and looks like this is the most elegant way to do that:

SELECT TOP(@MaxNumber) ROW_NUMBER() OVER (ORDER BY t1.number) 
FROM master..spt_values t1 CROSS JOIN master..spt_values t2 
EXCEPT
SELECT Id FROM <your_table>

Answer 6

from How do I find a "gap" in running counter with SQL?

select
    MIN(ID)
from (
    select
        100001 ID
    union all
    select
        [YourIdColumn]+1
    from
        [YourTable]
    where
        --Filter the rest of your key--
    ) foo
left join
    [YourTable]
    on [YourIdColumn]=ID
    and --Filter the rest of your key--
where
    [YourIdColumn] is null