[jsn]

> Feel free to correct me if there exists a RDBMS which can use an index on a "like."

huh? mysql does that for 'like' queries which don't start with a wildcard (that's exactly what you need for breadcrumbed trees).

also (i didn't read TFA, though) you don't have to use 'like'. you can use BETWEEN or just "path >= 'a' and path < 'b'", which, i suppose, uses index in even the most stupid RDBMS in the world).

prooflink log from my live real production database with a breadcrumbed tree: http://pastie.org/541611