Неявные JOIN-ы

Такие вот запросы практиковались в раннем Гедымине:

SELECT
   isg2.RDB$FIELD_NAME       FirstField
   , rc2.RDB$RELATION_NAME   NetTable
   , isg4.RDB$FIELD_NAME     SecondField
   , rc5.RDB$RELATION_NAME   TargetTable
   , isg6.RDB$FIELD_NAME     TargetField 
   , (SELECT 1
     FROM RDB$DATABASE
     WHERE
       EXISTS(SELECT *
              FROM RDB$RELATION_FIELDS rf
              WHERE rc5.RDB$RELATION_NAME = rf.RDB$RELATION_NAME
               AND rf.RDB$FIELD_NAME = 'LB')
       AND EXISTS(SELECT *
              FROM RDB$RELATION_FIELDS rf
              WHERE rc5.RDB$RELATION_NAME = rf.RDB$RELATION_NAME
               AND rf.RDB$FIELD_NAME = 'RB')) IsTree
 FROM
   RDB$INDEX_SEGMENTS isg1
   , RDB$RELATION_CONSTRAINTS rc1
   , RDB$REF_CONSTRAINTS rfc1
   , RDB$RELATION_CONSTRAINTS rc2
   , RDB$INDEX_SEGMENTS isg2
   , RDB$INDEX_SEGMENTS isg3
   , RDB$RELATION_CONSTRAINTS rc3
   , RDB$INDEX_SEGMENTS isg4
   , RDB$INDEX_SEGMENTS isg5
   , RDB$RELATION_CONSTRAINTS rc4
   , RDB$REF_CONSTRAINTS rfc2
   , RDB$RELATION_CONSTRAINTS rc5
   , RDB$INDEX_SEGMENTS isg6 
 WHERE
   rc1.RDB$RELATION_NAME = :tablename
   AND rc1.RDB$INDEX_NAME = isg1.RDB$INDEX_NAME
   AND rc1.RDB$CONSTRAINT_TYPE = 'PRIMARY KEY'
   AND rfc1.RDB$CONSTRAINT_NAME = rc2.RDB$CONSTRAINT_NAME
   AND rfc1.RDB$CONST_NAME_UQ = rc1.RDB$CONSTRAINT_NAME
   AND rc2.RDB$INDEX_NAME = isg2.RDB$INDEX_NAME
   AND rc1.RDB$RELATION_NAME <> rc2.RDB$RELATION_NAME
   AND isg3.RDB$FIELD_NAME = isg2.RDB$FIELD_NAME
   AND rc3.RDB$RELATION_NAME = rc2.RDB$RELATION_NAME
   AND rc3.RDB$CONSTRAINT_TYPE = 'PRIMARY KEY'
   AND rc3.RDB$INDEX_NAME = isg3.RDB$INDEX_NAME
   AND isg4.RDB$INDEX_NAME = isg3.RDB$INDEX_NAME
   AND isg2.RDB$FIELD_NAME <> isg4.RDB$FIELD_NAME
   AND isg5.RDB$FIELD_NAME = isg4.RDB$FIELD_NAME
   AND rc4.RDB$INDEX_NAME = isg5.RDB$INDEX_NAME
   AND rc4.RDB$CONSTRAINT_TYPE = 'FOREIGN KEY'
   AND rc4.RDB$RELATION_NAME = rc2.RDB$RELATION_NAME
   AND rfc2.RDB$CONSTRAINT_NAME = rc4.RDB$CONSTRAINT_NAME
   AND rfc2.RDB$CONST_NAME_UQ = rc5.RDB$CONSTRAINT_NAME
   AND rc5.RDB$INDEX_NAME = isg6.RDB$INDEX_NAME 

Возвращает список атрибутов типа множество для заданной таблицы.