PDO 数组中的重复值

我需要从数据库获取一些货币 ID，这是我的代码

$arr = [];

$currency_codes = array("USD", "RUB");
$currency_codes_in = implode(',', array_fill(0, count($currency_codes), '?'));
$query = "SELECT `curr_id` FROM `dictionary_currency` WHERE `curr_code` IN (". $currency_codes_in .")";
$stmt = $db->prepare($query); 
foreach ($currency_codes as $k => $id) {
    $stmt->bindValue(($k+1), $id);
}

$stmt->execute();
$currencies = $stmt->fetchAll();

foreach($currencies as $currency)
{
    foreach($currency as $key => $value)
    {
        $arr[] = $value;
    }
}
print_r($arr);
exit();

this is $currencies array

Array
(
    [0] => Array
        (
            [curr_id] => 643
            [0] => 643
            [curr_code] => RUB
            [1] => RUB
        )

    [1] => Array
        (
            [curr_id] => 840
            [0] => 840
            [curr_code] => USD
            [1] => USD
        )

)

这是$arr

Array
(
    [0] => 643
    [1] => 643
    [2] => 840
    [3] => 840
)

我不明白为什么我在数组中得到重复的值以及如何防止它？

PDO 是一个数据库包装器，可以为您做很多事情。例如，

• 在execute() 中绑定输入值
• 让您以所需的格式返回数据 https://phpdelusions.net/pdo#column

因此，实际上您需要的代码比现在少两倍：

$currency_codes = array("USD", "RUB");
$currency_codes_in = implode(',', array_fill(0, count($currency_codes), '?'));
$query = "SELECT `curr_id` FROM `dictionary_currency` WHERE `curr_code` IN ($currency_codes_in)";
$stmt = $db->prepare($query); 
$stmt->execute($currency_codes);
$arr = $stmt->fetchAll(PDO::FETCH_COLUMN);

或者我宁愿建议让它像

$query = "SELECT curr_code, curr_id FROM dictionary_currency WHERE `curr_code` IN ($currency_codes_in)";
$stmt = $db->prepare($query); 
$stmt->execute($currency_codes);
$arr = $stmt->fetchAll(PDO::FETCH_KEY_PAIR);