sqlite - How to find a gap in range in SQL -

this question explains how find first "unused" number in table, how can find same can define constraints. how alter query first unused number after that's greater 100

e.g. if have 23, 56, 100, 101, 103 in table should 102.

in mysql , postgresql

select  id + 1    test mo   not exists         (         select  null            test mi            mi.id = mo.id + 1         ) , mo.id> 100 order         id limit 1 

fiddle mysql , fiddle postgresql

in ms sql

select  top 1         id + 1    test mo   not exists         (         select  null            test mi            mi.id = mo.id + 1         )           , mo.id > 100 order         id 

fiddle