With sql find next available integer within range that is not present in existing integer subset(s)

Question

Problem statement:

given a range x -> y of unsigned integers
where x and y are both in the range

Answer 1

I am a little unclear on what your data really looks like. The problem statement, although well-formulated, seems to have little relationship with the query.

Let me assume that dhcp_range has the data. The query that you want is:

SELECT COALESCE(MIN(dr.end_address) + 1, 0)
FROM dhcp_range dr
WHERE NOT EXISTS (SELECT 1
                  FROM dhcp_range dr2
                  WHERE dr.end_address + 1 BETWEEN dr.start_address AND dr.end_address
                 );