$rs = Doctrine_Query::create()
            ->select('c.id, h.hours as hrs')
            ->from('Calculation c')
            ->innerJoin('c.History h')
            ->execute([], Doctrine_Core::HYDRATE_ARRAY);

var_dump($rs);

/*
// After the commit we get:
array(1) {
    [0]=> array(2) {
        ["id"]=> string(5) "1"
        ["hrs"]=> string(4) "3.00"
    }
} 

// Before it was this (and therefore also the expected result):
array(1) {
     [0]=> array(3) {
         ["id"]=> string(5) "1"
         ["hrs"]=> string(4) "3.00"
         ["History"]=> array(2) {
             [0]=> array(2) {
                 ["id"]=> string(4) "1"
                 ["hrs"]=> string(4) "3.00"
             }
             [1]=> array(2) {
                 ["id"]=> string(3) "2"
                 ["hrs"]=> string(4) "2.00"
             }
         }
     }
} 
*/