test.txt

<?php
$host = 'localhost';
$username = 'root';
$passwd = 'PhongDP25#*';
$dbname = 'online_shopping';
$conn = new mysqli($host, $username, $passwd, $dbname);

$query = "SELECT * FROM category order by name";

$data = $conn->query($query);
$newline = '<br/>';
echo "<form method='GET'>";
echo "<select id='category_list' name='cat_id' onchange='this.form.submit()'>";
echo "<option>Vui long chon category</option>";
while ($row = $data->fetch_assoc()) {
    $id = $row['Id'];
    $name = $row['Name'];
    echo "<option value='$id'>";
    echo "$name";
    echo "</option>";
}
echo "</select>";
echo "</form>";

if (isset($_GET['cat_id'])) {
    $cat_id = $_GET['cat_id'];
    $query = "SELECT p.id, p.Name, c.Name as Cat_name, p.Description, p.Price, p.Is_active
        from product p join category c
	on p.Cat_id = c.Id
        where p.cat_id = $cat_id
    order by p.Name";

    $data = $conn->query($query);
    echo "<table>
        <col style=\"width:20%\">
        <col style=\"width:20%\">
        <col style=\"width:20%\">
        <col style=\"width:20%\">
        <col style=\"width:20%\">
    <thead>
        <tr>
            <th>Name</th>  
            <th>Category</th>
            <th>Description</th>
            <th>Price</th>
            <th>Active</th>
        </tr>
    </thead>
    <tbody>";
    while ($row = $data->fetch_assoc()) {
       $name = $row['Name'];
       $cname = $row['Cat_name'];
       $des = $row['Description'];
       $price = $row['Price'];
       $is_active = $row['Is_active'];
       
       echo "<tr><td>$name</td>  
            <td>$cname</td>
            <td>$des</td>
            <td>$price</td>
            <td>$is_active</td></tr>";
    }
    
    echo "</tbody></table>";
}

$conn->close();
?>

<style>
    table, thead, tbody, tr, th, td{
        border: 1px solid black;
    }

</style>