Insert array to mysql database php

I want to add an array to my db. I have set up a function that checks if a value in the db (ex. health and money) has changed. If the value is diffrent from the original I add the new value to the $db array. Like this $db['money'] = $money_input + $money_db;.

function modify_user_info($conn, $money_input, $health_input){
(...)
if ($result = $conn->query($query)) {   
    while ($user = $result->fetch_assoc()) {
        $money_db = $user["money"];
        $health_db = $user["health"];
    }
    $result->close();

    //lag array til db med kolonnene som skal fylles ut som keys i array
    if ($user["money"] != $money_input){
        $db['money'] = $money_input + $money_db;
        //0 - 20
        if (!preg_match("/^[[0-9]{0,20}$/i", $db['money'])){
            echo "error"; 
            return false; 
        }

    }
    if ($user["health"] != $health_input){
        $db['health'] = $health_input + $health_db;
        //0 - 4
        if (!preg_match("/^[[0-9]{0,4}$/i", $db['health'])){
            echo "error"; 
            return false; 
        }   
        if (($db['health'] < 1) or ($db['health'] > 1000))
        {
            echo "error"; 
            return false;       
        }
    }

The keys in $db represent colums in my database. Now I want to make a function that takes the keys in the array $db and insert them in the db. Something like this ?

$query = "INSERT INTO `main_log` ( `id` , ";
foreach(range(0, x) as $num) {

    $query .= array_key.", ";       
}
$query = substr($query, 0, -3); 
    $query .= " VALUES ('', "; 
    foreach(range(0, x) as $num) {

        $query .= array_value.", ";     
    }
    $query = substr($query, 0, -3); 
    $query .= ")";