TABLE_(TESTPARTNER)
  SERIAL_  (TESTPARTNER_ID) PRIMARY_KEY
  STRING_  (TESTPARTNER_NAME, 200) INDEX
  STRING_  (TESTPARTNER_ADDRESS, 200)
END_TABLE

TABLE_(TESTPRODUCT)
  SERIAL_  (TESTPRODUCT_ID) PRIMARY_KEY
  INT_  (Z) REFERENCES (TESTPARTNER)
  STRING_  (TESTPRODUCT_UNIT, 20)
END_TABLE

void PostgreSQLTest::ShowTestData() {
    Sql sql(m_session);
    sql.ClearError();
    sql * Select(TESTPRODUCT_UNIT)
    .From(TESTPRODUCT)
    .InnerJoin(TESTPARTNER)
    .On(Z.Of(TESTPRODUCT) == TESTPARTNER_ID.Of(TESTPARTNER));
    while(sql.Fetch())
        Cout() << sql[0];
 
 
}

select testproduct_unit from testproduct inner join testpartner on
 testpartner.testpartner_id = testproduct.z ;
 testproduct_unit
------------------
 wheededee
(1 row)