>Where is truly weak is that not extend the relational model to INNER values (so you can't "SELECT (SELECT chars FROM name)) but is a limitation of sql, not the

>Where is truly weak is that not extend the relational model to INNER values (so you can't "SELECT (SELECT chars FROM name)) but is a limitation of sql, not the relational model. True, but fortunately most database systems have proprietary ways to achieve some of that. For instance in PostgreSQL select * from regexp_split_to_table('abc', '') chars; gives you chars ------- a b c It's called table-valued functions and it's extensible. Obviously, it's not quite as general as what you are talking about because the values are not actually stored as tables. To get a bit closer to that you could use composite types and arrays. I'm not convinced it's worth the added complexity though.