为什么Mysql没有正确返回结果？

Question

我有以下代码：

    <?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();
}
?>

它应该返回329但是它在var_dump中返回null。

Mysql表Wg_Attack_troop，表明表中存在329：

wg_attack table：

正如您所看到的，代码是正确的，那为什么它会在var_dump中返回NULL？

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

80271是$ kaimo_id 32是$ troop_id

编辑NR2：phpmyadmin返回此

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