PDO duplicate values in array - php

Question

I need to get some currency ids from db, this is my code
$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
)
)
and this is $arr
Array
(
[0] => 643
[1] => 643
[2] => 840
[3] => 840
)
I don't understand why I get duplicate values in arrays and how to prevent it?

Answer 1

PDO is a database wrapper that can do many things for you. For example,
bind input values right in execute()
get you returned data already in the desired format
So in fact you need two times less code than you have now:
$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);
or I would rather propose to make it like
$query = "SELECT curr_code, curr_id FROM dictionary_currency WHERE `curr_code` IN ($currency_codes_in)";
$stmt = $db->prepare($query);
$stmt->execute($currency_codes);
$arr = $stmt->fetchAll(PDO::FETCH_KEY_PAIR);

Answer 2

The loop is problematic:
foreach($currencies as $currency) {
foreach($currency as $key => $value) {
$arr[] = $value;
}
}
Just use a simple
foreach($currencies as $currency) {
$arr[] = $currency[0];
}
Edit #1:
Using your $currencies and old query, I got the following:
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
)
)
Array
(
[0] => 643
[1] => 643
[2] => RUB
[3] => RUB
[4] => 840
[5] => 840
[6] => USD
[7] => USD
)

Answer 3

I know this question is getting old. But here is the solution to prevent the duplicate values from PDO.
Just using this:
$stmt->fetchAll(PDO::FETCH_ASSOC);
Instead of this:
$stmt->fetchAll();

Answer 4

use following query
$query = "SELECT DISTINCT curr_id FROM dictionary_currency WHERE curr_code IN (". $currency_codes_in .")";