Question

Note: The Data schema can not be changed. I’m stuck with it.

Database: SQLite

I have a simple tree structure, without parent keys, that is only 1 level deep. I have simplied the data for clarity:

ID    Content       Title
1     Null          Canada
2     25            Toronto
3     33            Vancouver
4     Null          USA
5     45            New York
6     56            Dallas

The structure is ordinal as well so all Canadian Cities are > Canada’s ID of 1 and less than the USA’s ID of 4

Question: How do I select all a nation’s Cities when I do not know how many there are?

Answer 1

select * from tbl
 where id > 1
   and id < (select min(id) from tbl where content is null and id > 1)

EDIT

I just realized the above does not work if there are no countries with greater ID. This should fix it.

select * from tbl a
 where id > 4
   and id < (select coalesce(b.id,a.id+1) from tbl b where b.content is null and b.id > a.id)

Edit 2 – Also made subquery fully correlated, so only have to change country id in one place.