How to add products to the cart of different pages?

I am making a cart, and I have 3 pages and 3 tables to insert products into this cart:

stock_mol_comp, stock_mol_trac, stock_mol_torcao

It worked perfectly when I only had compression page products. But now when I went to put the 3 pages to add to the cart does not work.

The cart works with $_SESSION variables, this is the code:

<a class='fa fa-cart-plus' href='cart.php?add=carrinho&id=".$row['id_mol_comp']."'></a>

cart.php:

<?php 
session_start(); 
if (!isset($_SESSION['itens'])){ 
    $_SESSION['itens']=array(); 
} 
if(isset($_GET['add'])&& $_GET['add']=="carrinho") { 
    $idproduto = $_GET['id']; 
    if(!isset($_SESSION['itens'][$idproduto])){ 
        $_SESSION['itens'][$idproduto]=1; 
    }else{ 
        $_SESSION['itens'][$idproduto]+=1; 
    } 
} 
header('location: carrinho.php'); 
?>

Then prints:

<?php 
if (!isset($_SESSION['itens'])){ 
    $_SESSION['itens']=array(); 
}
if (count($_SESSION['itens'])==0){
    echo'Carrinho vazio <br><a href="mol_compressao.php">Adicionar Itens</a>'; 
}else{
    echo"
  <h2>Resumo de Compras</h2>
  <br>
  <div align='start'>
    <div class='card mx-auto w-100'>
      <div class='container-fluid''>
        <div class='row align-items-end' style='height:40px;'>
            <div class='col-md-2' style='text-align: center'><h5>REFERÊNCIA</h5></div>
            <div class='col-md-3' style='text-align: center'><h5>QUANTIDADE</h5></div>
            <div class='col-md-3' style='text-align: center'><h5>PREÇO UNITÁRIO</h5></div>
            <div class='col-md-2' style='text-align: center'><h5>PREÇO TOTAL</h5></div>
          </div>
        </div> 
        <hr>";
    include ("db.php");
    $precototali=0;
    foreach($_SESSION['itens'] as $idproduto => $quantidade){

        $select_car = "SELECT * FROM stock_comp WHERE id_mol_comp=$idproduto";
        $result =  mysqli_query($con, $select_car);
        $rows = array();                     


        $select_car2 = "SELECT * FROM stock_torcao WHERE id_mol_torcao=$idproduto";
        $result =  mysqli_query($con, $select_car2);
        $rows = array();

        $select_car1 = "SELECT * FROM stock_trac WHERE id_mol_trac=$idproduto";
        $result =  mysqli_query($con, $select_car1);
        $rows = array();

        while ($row = $result->fetch_assoc()) {
            $rows[] = $row;
            $precototal=$row['preco']*$quantidade;   

            $precototali+=$precototal;
            $precoiva=$precototali*1.23;  

        echo "
        <div class='card-body'>
            <div class='row align-items-center' style='height:0px;'>
                <div class='col-md-2' style='text-align: center'>$row[referencia]</div>
                <div class='col-md-3' style='text-align: center'><i style='font-size:18px' id='diminuir' class='fa'>&#xf147;</i>&nbsp&nbsp$quantidade&nbsp&nbsp<i style='font-size:18px' id='aumentar'class='fa'>&#xf196;</i></div>
                <div class='col-md-3' style='text-align: center'> ".number_format($row['preco'],2,",",".")." €</div>
                <div class='col-md-2' style='text-align: center'> ".number_format($precototal,2,",",".")." €</div>
             <div class='col-md-2' style='text-align: center'><i class='fa fa-remove' style='font-size:24px'></i></div>

            </div>
        </div>";
        }           
    }
    echo "
        <br>
            <div class='col-md-11' style='text-align: end'><h4>Total(s/IVA): ".number_format($precototali,2,",",".")." €</h4></div> 

            <div class='col-md-11' style='text-align: end'><h2>Total(c/IVA): ".number_format($precoiva,2,",",".")." €</h2></div> 
                        <br>";
 }
 echo"<hr>";
 ?>

But this way, just print the product with the id of the last select , in this case this select: (if I change the order the select will print what I put in last place)

 $select_car1 = "SELECT * FROM stock_trac WHERE id_mol_trac=$idproduto";
 $result =  mysqli_query($con, $select_car1);
 $rows = array();

For example:

When I have the cart empty and I'm going to add a product's page traction (which is the select that is in last) it adds correctly, but then when I'm going to add a product's page compression it increases the product's page traction.