Verifying post value with database

Verifying post value with database

I know some of you might not agree with this but Its good to do. Below you
will find my two tables.
Table Item
pid Name
1 cat
2 dogs
3 cows
Table Category
CatID pid Name
11 1 banana
33 1 apple
44 2 strawberry
Basically I have a Select option and the option might looks like the one
below
<option selected="" value="33">apple</option>
now if I was to change the value to a letter or number or leave it blank
value=""
Then I click on my submit button.
In the page which I am posting to I have
if(isset($_POST['pid']) && isset($_POST['length']) && isset($_POST['Qty'])
&& isset($_POST['Category'])){
$pid = $_POST['pid'];
$length = $_POST['length'];
$qty = $_POST['Qty'];
$Category = $_POST['Category'];
$wasFound = false;
<-I have a query here ->
<-I have another if statement here which should run if everything is okay ->
}
<-I have a query here -> this is where my problem is
I have an individual query which should change with the database to verify
that what the user is posting is in the database. This is general to make
sure that the user have not done something that they should not have.
dbconnect();
$statement = $db->prepare("
SELECT * FROM Category WHERE CatID =:Cat
LIMIT 1
");
$statement->bindParam('Cat',$Category);
$statement->execute();
$statement->fetchAll(PDO::FETCH_ASSOC);
if ($statement->rowCount() > 0) {
exit();
}
I have run query both when I have change the value and it doesn't prove
the item getting add to the cart BUT even when I haven't change anything,
it still doesn't work. I do not get an error