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;