Mysqli num row返回不起作用

Question

I'm wondering why it is not working for mysqli eventhou mysql_num_row is working.

if (mysql_num_rows($rows) > 0) {
    echo "<p>That name has been taken </p>";
}

That is mysql. But, Im trying convert it to mysqli.

 if (mysqli_num_rows($rows) > 0) {
        echo "<p>That name has been taken </p>";
    }

It supposed to be displayed on the screen but it's not. And there is nothing error message displayed. Or am I missing something? Any ideas?

Answer 1

First, a quick tutorial on some of the differences between mysql_* and mysqli_* functions.

In mysql_* you would have 3 parameters for your DB connection, then have a seperate line for your DB selection.

For example:

$db = mysql_connect("host","username", "password");
$db_selected = mysql_select_db('db_name', $db);
if (!$db_selected) {
    die ('Can\'t use this : ' . mysql_error());
}

Your query would come first, followed by your DB connection.

For example:

mysql_query($query,$db);

But in mysqli_* things have changed including the parameters location. You now put all 4 parameters, for example (if you haven't done so yet):

$db = new mysqli("host","username", "password", "db_name");

if (mysqli_connect_errno()) {
printf("Connect failed: %s
", mysqli_connect_error());
exit();
}

then the DB connection would come first, followed by the query instead of the other way around:

mysqli_query($db,$query);

A sample query:

$email = mysqli_real_escape_string($db,$_POST['email']);
$query = mysqli_query($db, "SELECT * FROM table_name WHERE email='".$email."'");

if(mysqli_num_rows($query) > 0){

    echo "email already exists";
}else{
    $sql="INSERT INTO table_name (email) VALUES ('$email')";
    if (!mysqli_query($db,$sql))
    {
        die('Error: ' . mysqli_error($db));
    }
}