使用$ SESSION变量动态替换php语句中的变量

I’m playing around with mysql databases, and more specifically, relational tables for the first time and am looking for some guidance. It is structured as so:

   Database: DV501 (containing 3 tables (for now))

       models01 (holds each car model and gives them an id)
          - model_id
          - model_name

       int01 (holds the parts, names, prices, etc…)
          - id
          - part_no
          - part_name
          - part_cost
          - part_total
          etc…

       camry01 (used as relational table between models01 and parts in int01 that fit this car)
          - id
          - model_id
          - part_id

For the web page, I have a form with a dropdown containing car models, each car in the dropdown has a value that corresponds to it’s model_id in the database. Camry has a value of ‘1’ and a model_id of ‘1’, Corolla a value of ‘2’ and a model_id of ‘2’ and so on…

When you submit the form, it stores the selected value in $_SESSION[‘selected_car’] variable to access later.

(This is where I am getting stuck)
When the next page loads after the form is submitted, it should display only parts from table ‘int01’ that fit the car stored in the session variable.

I was using the statement below to work from, but as you can see I’m telling it to use camry01 table where as I want to dynamically use the value stored in the $_SESSION[‘selected_car’] to choose the correct model, and display the parts that fit it.

<?php
   $servername = "localhost";
   $username = "root";
   $password = "root";
   $dbname = "DV501";

   // Create connection
   $conn = mysqli_connect($servername, $username, $password, $dbname);
   // Check connection
   if (!$conn) {
       die("Connection failed: " . mysqli_connect_error());
   }

   $sql = "SELECT camry01.model_id, camry01.part_id, int01.part_name, int01.part_no, int01.part_total
    FROM camry01
        LEFT JOIN int01 ON (int01.id = camry01.part_id)
        WHERE (camry01.model_id = '1');";


   $result = mysqli_query($conn, $sql);

   if (mysqli_num_rows($result) > 0) {
       // output data of each row
       while($row = mysqli_fetch_assoc($result)) {

   echo $_SESSION['selected_car'] . " - " . $row['part_name'] . " - Price: " . $row['part_total'] . "<br/>";

      }
   }  



   else {
      echo "0 results";
   }

mysqli_close($conn);
?>

Any help would be greatly appreciated.

You can get the variable name from SESSION and bind it in the query so that you can fetch the desired the result.

$stmt = $conn->prepare("SELECT camry01.model_id, camry01.part_id, int01.part_name, int01.part_no, int01.part_total
FROM camry01 LEFT JOIN int01 ON (int01.id = camry01.part_id) WHERE (camry01.model_id = ?)");
$stmt->bind_param("i", $_SESSION[‘selected_car’]);
$stmt->execute();

$stmt->close();
$conn->close();