Notice: Trying to get property 'num_rows' of non-object in line 35

Question

I don't understand this. I want to get a string from database and add it to another string to fetch results.

if (isset($_POST['key'])) {
    $conn = new mysqli('localhost', 'root', '', 'ams');
    if ($_POST['key'] == 'getStudentsData') {
        $start = $conn->real_escape_string($_POST['start']);
        $limit = $conn->real_escape_string($_POST['limit']);
        $set = $conn->query("SELECT * from teachers where id =$uid");
        $dat = $set->fetch_array();

        $dat = join(', ', $dat);
        $sql = $conn->query("SELECT * FROM logins WHERE subject IN $dat LIMIT $start, $limit");
        if (!empty($sql) && $sql->num_rows > 0) {
            $response = "";
            while ( $data = $sql->fetch_array(MYSQLI_ASSOC)) {
                $response .= '
                        <tr class="text-center">
                            <td>' . $data["fname"] . '&nbsp' . $data["lname"] . '</td>
                            <td>' . $data["matno"] . '</td>
                            <td>' . $data["email"] . '</td>
                            <td>' . $data["phone_no"] . '</td>
                            <td class="text-center">
                                <button value="Edit" class="btn btn-primary"> ' . $user->i('upload') . '</button>
                                <button value="View" class="btn">' . $user->i('eye') . '</button>
                                <button value="Delete" class="btn btn-danger">' . $user->i('trash') . '</button>
                            </td>
                        </tr>
                    ';
            }
            exit($response);
        } else
            exit('reachedMax');
    }
}

Error is this:

Notice: Trying to get property 'num_rows' of non-object in line 35

This line `$sql = $conn->query("SELECT * FROM logins WHERE subject IN $dat LIMIT $start, $limit");` isn't returning a valid result, and so you're not able to use `->num_rows()` on the result set. — Winch, Jun 14 '18 at 15:32

score 0 · Answer 1 · answered Oct 03 '18 at 13:26

You need braces for the IN! which will correct your sql statement. Still i would suggest you to add a check for the $dat before pass to the sql query whether it is not empty.

$conn->query("SELECT * FROM logins WHERE subject IN ($dat) LIMIT $start, $limit");

then best practice is check your query result is true or false explicitly

 if ($sql === false) {
     exit('reachedMax');
 }
 //come here if the query is successfully executed

What is the reason to down vote? – Ntwobike Aug 30 '19 at 09:05 — Ntwobike, Aug 30 '19 at 09:05

score 0 · Answer 2 · edited Jun 01 '19 at 11:08

I had the same problem previously.

 $q1 =  "SELECT * ".
            "FROM admin, student ".
            "WHERE admin.pcode = student.code AND admin.puser_name = student.puser_name AND admin.id IN (SELECT admin.id FROM admin ORDER BY admin.id DESC LIMIT 1) ";

The problem is due to LIMIT. I don't know why it says error when I put LIMIT over there and the error disappears when I remove Limit from the query

Notice: Trying to get property 'num_rows' of non-object in line 35

2 Answers2

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