为什么Mysql没有正确返回结果？

Question

I have the following code:

    <?php
function GetSumPresentTroop3($kaimo_id, $troop_id){ // ZN kodas
global $db, $wg_village, $user;
$underaway = 0;

$sql="SELECT 
            wg_attack_troop.id
        FROM
            wg_attack ,
            wg_attack_troop
        WHERE
            wg_attack.id =  wg_attack_troop.attack_id AND
            wg_attack.status = '0' AND
            wg_attack.village_attack_id =  '".$kaimo_id."' AND
            wg_attack_troop.troop_id =  '$troop_id'
        GROUP BY 
            wg_attack_troop.id";

$db->setQuery($sql);
return $db->loadResult();
}
?>

And it should return 329 but insteed it returns a null in var_dump.

Mysql table Wg_Attack_troop which shows that 329 exists in the table:

wg_attack table:

As you can see code is correct, then why does it return a NULL in var_dump?

EDIT NR1: Var_dump: string(5) "80271" string(2) "32" NULL

80271 is $kaimo_id 32 is $troop_id

Edit NR2: phpmyadmin returns this

SELECT wg_attack_troop.id
FROM wg_attack, wg_attack_troop
WHERE wg_attack.id = wg_attack_troop.attack_id
AND wg_attack.status = '0'
AND wg_attack.village_attack_id = '80271'
AND wg_attack_troop.troop_id = '32'
GROUP BY wg_attack_troop.id
LIMIT 0 , 30