Insert Into Query Failed in PHP - php

Question

I am new in PHP and I'm currently working with a module of Setting an operation wherein I will insert data from a modal into the database. There's no error in terms of getting the data but when I click the button, the "Query failed: INSERT INTO tbl_mobilvis (location, timestart, timeend, mobilnum) VALUES ('vbv','12:09','17:09','4')" always being displayed.
Here's the code for the db class..
var $hostname = "REDACTED";
var $username = "REDACTED";
var $password = "REDACTED";
var $database = "REDACTED";
function select_db() {
$result = mysqli_connect($this->hostname,$this->username,$this->password);
if (!mysqli_select_db( $result, $this->database)) {
echo 'Selection of database: '.$this->database.' failed.';
return false;
}
}
function query($query) {
$result1 = mysqli_connect($this->hostname,$this->username,$this->password);
$result = mysqli_query($result1,$query) or die("Query failed: $query<br><br>" . mysql_error());
return $result;
mysql_free_result($result);
}
function fetch_array($result) {
return mysqli_fetch_array($result);
}
function num_rows($result) {
return mysqli_num_rows($result);
}
function last_insert_id() {
return mysqli_insert_id();
}
function kill() {
mysqli_close();
}
}
?>
and here's the code for inserting the data.
<?php
if (isset($_POST['btnSubmit'])) {
$db = new mysqldb();
$db->select_db();
$result1 = mysqli_connect("REDACTED","REDACTED","REDACTED");
$sql_mobilvis = sprintf("INSERT INTO tbl_mobilvis (location, timestart, timeend, mobilnum) VALUES ('%s','%s','%s','%s')",
mysqli_real_escape_string($result1,$_POST['location']),
mysqli_real_escape_string($result1,$_POST['starttime']),
mysqli_real_escape_string($result1,$_POST['endtime']),
mysqli_real_escape_string($result1,$_POST['mobilnum']));
$result_user = $db->query($sql_mobilvis);
if ($_POST['fields']){
$inserted_mobilvis_id = $db->last_insert_id();
foreach ( $_POST['fields'] as $key=>$value ) {
$sql_enforcer = sprintf("INSERT INTO tbl_mobilenforcer (enforcername) VALUES ('%s')",
mysqli_real_escape_string($result1, $value) );
$result_website = $db->query($sql_enforcer);
$inserted_enforcer_id = $db->last_insert_id();
$sql_mobil_enforcer = sprintf("INSERT INTO tbl_mobil (mobilid, mobilenforcerid) VALUES ('%s','%s')",
mysqli_real_escape_string($result1,$inserted_mobilvis_id),
mysqli_real_escape_string($result1,$inserted_enforcer_id) );
$result_mobil_enforcer= $db->query($sql_mobil_enforcer);
}
} else {
echo "<script>alert('no added enforcers')</script>";
}
echo "<h1>User Added, <strong>" . count($_POST['fields']) . "</strong> enforcers are added!</h1>";
$db->kill();
}
?>
Why I am getting this Query failed?