what is HSQL for the following example, with subquery in select clause?
what is the rule for the native sql <-> hibernate sql conversion?

For example, native sql is:
select a.name, (select b.desc from table2 b where b.code = a.code) as desc
from table 1 a

Subselects in the select clause are not supported in HQL in the current version. Map a class property with the "formula" attribute.

I think you can select the same with left join too.