php - mysqli_query() expects at least 2 parameters & mysqli_query(): Empty query error messages

I got 4 errors while running this code that add the email address of the user to the database called ecommerce in the table called subscriptions.

$con = new mysqli('localhost', 'root', '','ecommerce');

if (!$con) {
    die('Could not connect: ' . mysql_error());
}    

$errors = array();
if($_POST)
    {

        if(empty($_POST['email']))
        {
            $errors['email1'] = "
Dont forget to write your email!
";
        }else {
            $email = test_input($_POST["email"]);

            // check if e-mail address is well-formed
            if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
                $errors['email2'] = "
Something wrong is with your email
"; 
            }else{


                // check if the email already exists
                $query = mysqli_query("SELECT * FROM subscriptions WHERE email='$email'");
                if(mysqli_num_rows($query) > 0){
                    $errors['email3'] = "
Your had been registered before!
";
                }
            }
        }

        //check errors

        if(count($errors) == 0)
        {
            $insert_email = mysqli_query("INSERT INTO subscriptions (email) VALUES ('$email')");
            $insert_email = mysqli_query($con, $insert_email);
            $success = "";
        }
    }

function test_input($data) {
   $data = trim($data);

   $data = stripslashes($data);
   $data = htmlspecialchars($data);
   return $data;
}
?>

                                
                                
                                

                                


                                

                                

                                You can add your email to our emailsshow list.
";}?>

The errors are like this:

Warning: mysqli_query() expects at least 2 parameters, 1 given on line 27

Line 27:

$query = mysqli_query("SELECT * FROM subscriptions WHERE
email='$email'");

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, null given on line 28

Line 28:

if(mysqli_num_rows($query) > 0){

Warning: mysqli_query() expects at least 2 parameters, 1 given on line 37

Line 37:

$insert_email = mysqli_query("INSERT INTO subscriptions (email) VALUES ('$email')");

Warning: mysqli_query(): Empty query on line 38

Line 38:

$insert_email = mysqli_query($con, $insert_email);

I'm new at this forum and it would best if you can help me with that cause I really do know to do ... thanks in advance!

Answer

Instead of

$query = mysqli_query("SELECT * FROM subscriptions WHERE email='$email'");

use

$query = $con->query("SELECT * FROM subscriptions WHERE email='$email'");

or

$query = mysqli_query($con, "SELECT * FROM subscriptions WHERE email='$email'");

Also instead of

$insert_email = mysqli_query("INSERT INTO subscriptions (email) VALUES ('$email')");

use

$insert_email = $con->query("INSERT INTO subscriptions (email) VALUES ('$email')");

These are the only 2 errors that I could see.