How do i do a efficient HSQL join between 2 tables without specific relation in a mapping?

I have 2 tables where i want to know the description on a table A with a field on a table B.

Table A (fields)
regnumberA
description
regdate


Table B
regnumberB
stnumber
regdate

i want to know how i obtain de field description of a table A if i want to relate de stnumber to obtain this description if stnumber=regnumberA to obtain these description using the better form to build it with HSQL, help me please.

Regards.

HQL does not support arbitrary joins between entities. If there is an association there then map it.