如何修复mysqli_query（）和mysqli_fetch_array（）错误

Question

I'm trying to make a PHP script that prints text from file to website on button click.

This is my code:

<?php
    mysqli_connect("host", "username", "password", "dbname");
    if (isset($_POST['button'])) {
        mysqli_query("SELECT name,lastname FROM users ORDER BY RAND()");
        $name = null;
        $lastname = null;
        while ($row = mysqli_fetch_array()) {
            $name = $row['name'];
            $lastname = $row['lastname'];
        }
        echo '<p><small>Output:</small></p><pre style="min-width:auto;display:table;">' . $name . '_' . $lastname . '</pre>Format: <b>name_lastname</b> <span style="width:310px;">';
    }
?>
<form method="POST">
    <button type="submit" class="btn btn-default" name="button">button</button>
    <br>
</form>

And this is the error that I get every time when the button is clicked:

Anyone knows how to fix this?

Answer 1

You need to introduce database connection variable which most mysqli_* functions required, $con in your modified script:

<?php
    $con = mysqli_connect("host", "username", "password", "dbname") or die(mysqli_error($con));
    if (isset($_POST['button'])) {
        $result = mysqli_query($con, "SELECT name,lastname FROM users ORDER BY RAND()");
        $name = null;
        $lastname = null;
        while ($row = mysqli_fetch_array($result)) {
            $name = $row['name'];
            $lastname = $row['lastname'];
        }
        echo '<p><small>Output:</small></p><pre style="min-width:auto;display:table;">' . $name . '_' . $lastname . '</pre>Format: <b>name_lastname</b> <span style="width:310px;">';
    }
?>
<form method="POST">
    <button type="submit" class="btn btn-default" name="button">button</button>
    <br>
</form>

In addition you need to pass result set identifier returned by mysqli_query(), $result in that case. Everything can be found at W3Schools.