Resolve MySQLi empty query error [duplicate] - php

Question

This question already has an answer here:
What to do with mysqli problems? Errors like mysqli_fetch_array(): Argument #1 must be of type mysqli_result and such
(1 answer)
Closed 6 years ago.
Warning received:
Warning: mysqli::query(): Empty query in C:\wamp\www\otp-task\welcome.php on line 62
My database connection is here:
function insertDB($email, $OTP , $phonenumber )
{
$servername = "localhost";
$username = "root";
$password = "";
$db = "dbotp";
$conn = new mysqli($servername, $username, $password, $db);
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
// insert to db and close the connection, default time attribute is 60 mins
// the table name is onetime and will hold the otp and phonenum and email
$res = mysqli_query($conn, "INSERT INTO onetime (otpnum,email,phoneNum,action) VALUES ('$OTP' , '$email' , '$phonenumber','success')");
// $res = "INSERT INTO onetime (otpnum,email,phoneNum,action) VALUES ('$OTP' , '$email' , '$phonenumber', 'success')";
if ($conn->query($res) === TRUE) {
echo "New record created successfully";
} else {
echo "Error: " . $res . "<br>" . $conn->error;
}
$conn->close();
}

Answer 1

The following two is just a different format for the same thing:
$conn->query(...)
and
mysqli_query($conn, ...)
Once you executed one of them, use the return value of it instead of re-executing the query:
$res = $conn->query(...)
if ($res) {
// ...
}
Please also read about prepared statements: http://php.net/manual/en/mysqli-stmt.prepare.php