Check if already a user then insert into the database php - php

Question

My code works, if I wish to insert into the database, but my checking whether the user already exists doesn't work.
*I thought the idea was to check if a row exists already with that username, if so don't add that user to the database, else
$email = $_POST['email'];
$password= password_hash($_POST['password'], PASSWORD_BCRYPT, $options);
$username= $_POST['username'];
$result = mysqli_query($mysqli, "SELECT username FROM users WHERE username = '$username'");
$row_count = $result->num_rows;
if($row_count == 1){
echo'User exists';
}else{
$query = "INSERT INTO users (username, email, password) VALUES(?, ?, ?)";
$statement = $mysqli->prepare($query);
//bind parameters for markers, where (s = string, i = integer, d = double, b = blob)
$statement->bind_param('sss', $username, $email, $password);
if($statement->execute()){
print 'Success! ID of last inserted record is : ' .$statement->insert_id .'<br />';
}else{
die('Error : ('. $mysqli->errno .') '. $mysqli->error);
}
$statement->close();
}

Answer 1

You have mixed the Procedural style & Object oriented style for executing the query.
When using,
1) Procedural Style
$result = mysqli_query($mysqli, "Your Query");
use this, $row_count = mysqli_num_rows($result);
2)Object oriented style
$result = $mysqli->query("Your Query");
Use this, $row_count = $result->num_rows;
So, According to your code, You are using Object Oriented Style. So, you need to change
$result = mysqli_query($mysqli,"SELECT username FROM users WHERE username = '$username'");
to
$result = $mysqli->query("SELECT username FROM users WHERE username = '$username'");
Edited Code.
$email = $_POST['email'];
$password= password_hash($_POST['password'], PASSWORD_BCRYPT, $options);
$username= $_POST['username'];
$result = $mysqli->query("SELECT username FROM users WHERE username = '$username'");
$row_count = $result->num_rows;
if($row_count == 1)
{
echo 'User exists';
}
else
{
$query = "INSERT INTO users (username, email, password) VALUES(?, ?, ?)";
$statement = $mysqli->prepare($query);
//bind parameters for markers, where (s = string, i = integer, d = double, b = blob)
$statement->bind_param('sss', $username, $email, $password);
if($statement->execute())
{
print 'Success! ID of last inserted record is : ' .$statement->insert_id .'<br />';
}
else
{
die('Error : ('. $mysqli->errno .') '. $mysqli->error);
}
$statement->close();
}
For more info, check this mysqli_num_rows vs ->num_rows

Answer 2

$db = ("SELECT username FROM userlist WHERE username='$username'");
$query = $conn->query($db);
if(mysqli_fetch_array($query) > 0 ) { //check if there is already an entry for that username
echo "Username already exists!";
}