TRUE if a solution was found, or FALSE to
indicate the query could not be proven. This function may be called
repeatedly until it fails to generate all solutions to the query. The
return value
PL_S_NOT_INNER is returned if qid is not the
innermost query.
If the PL_open_query()
had the flag PL_Q_EXT_STATUS, there are additional return
values (see section
12.4.1.2).