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

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