Is there something wrong with this Query? New to mysqli commands - mysqli

Question

Is there something wrong with this query in mysqli? I converted it from mysql, worked perfectly then but now it doesn't
mysqli_query($con,"SELECT * FROM signed_out_students WHERE date = '$date6' AND time_in = '' order by time_out DESC");
This is how it fits into the actual code. I know that there is entries in the databse with the date of today but its not showing them? D:
else if (out == $display) {
date_default_timezone_set('NZ');
$date6 = date('d.m.Y');
$result4 = mysqli_query($con,"SELECT * FROM signed_out_students WHERE date = '$date6' AND time_in = '' order by time_out DESC");
echo '<table border="0">';
echo '<tr>';
echo '<td width="70px"><h2>Date</h2>';
echo '</td>';
echo '<td width="150px"><h2>Name</h2>';
echo '</td>';
echo '<td width="90px"><h2>Form Class</h2>';
echo '</td>';
echo '<td width="70px"><h2>Time Out</h2>';
echo '</td>';
echo '<td width="70px"><h2>Time In</h2>';
echo '</td>';
while($row4 = mysqli_fetch_array($result4))
{
echo '<tr>';
echo '<td><p>' . $row4['date'];
echo '</td>';
echo '<td><p>' . $row4['name'];
echo '</td>';
echo '<td><p>' . $row4['form_class'];
echo '</td>';
echo '<td><p>' . $row4['time_out'];
echo '</td>';
echo '<td><p>' . $row4['time_in'];
if ($row['time_in'] == "") { echo '-';}
echo '</td>';
}
echo '</table>';
}
Thanks guys!

Answer 1

Is there something wrong with this query in mysqli?
Yes, a lot.
You aren't checking for errors
You aren't using placeholders
You're using mysqli, while PDO have to be used instead.
Start here: https://stackoverflow.com/tags/pdo/info
Also, as a side note, your date have to be in 'Y-m-d' format.

Answer 2

remove the single quotes from the variable in the Query :
mysqli_query($con,"SELECT * FROM signed_out_students WHERE date = $date6 AND time_in = '' order by time_out DESC");