$db = M();
$db->startTrans();
$result1 = $db->Table('db_a')->setInc('field_1', 120);
$result2 = $db->Table('db_b')->setDec('field_1', 110);
if($result1 && $result2){
//提交
$db->commit();
}
else{
//回滚
$db-<rollback()
}
$db = M();
$db->startTrans();
$result1 = $db->Table('db_a')->setInc('field_1', 120);
$result2 = $db->Table('db_b')->setDec('field_1', 110);
if($result1 && $result2){
//提交
$db->commit();
}
else{
//回滚
$db-<rollback()
}