从MySql DB中的URL获取数据

Question

I would like to take data from DB via simple script

<a href='category.php?CAT=Shoes'>Shoes</a> 

then simple show all rows with the specific data in "CAT" column like this:

$CAT = $_GET['CAT'];
    $sql = "SELECT * FROM Shop WHERE CAT = $CAT" ;
       $result = $conn->query($sql);
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) { 
echo"
... results
"}}

The problem is that this script does work with INT (for example SELECT CAT = 5 like category.php?CAT=5) but not with VARCHAR (SELECT CAT = Shoes like category.php?CAT=Shoes). Now I'm not sure why is this happening. With Error: Trying to get property of non-object

Answer 1

$sql = "SELECT * FROM Shop WHERE CAT = '$CAT'"