下载PHP而不是运行

Question

我正在尝试创建一个将数据提交到mySQL工作台上的数据库的表单。每当我单击提交时，它最终都会下载php文件而不是运行它。所有文件都在同一文件夹中。

inventorylog.html

<form action="insert.php" method="post">
    <input required type="text" name="sku_input" placeholder="Sku #" />
    <br>
    <input value="Add Sku" type="submit" name="submit" />
  </form>

connect.php

<?php
    $host="localhost";
    $port=3306;
    $socket="/tmp/mysql.sock";
    $user="root";
    $password="";
    $dbname="Logs";

    $con = mysqli_connect($host, $user, $password, $dbname, $port, $socket)
        or die ('Could not connect to the database server' . mysqli_connect_error());   

    //$con->close();
?>

insert.php

<?php
    /*Needs the connection object created in the connect.php file to work*/
    header("LOCATION:inventorylog.html");
    require('connect.php');
    /*require('inventorylog.html');*/

    /*Data from the html form is on the right. The objects that will be composed of that data is on the left.*/
    if(isset($_POST['submit'])) {
    $skunum = mysqli_real_escape_string($con, $_POST['sku_input']);
    echo 'sku_input';

    $sql = "INSERT INTO skulist (sku_input) 
                          VALUES ('$skunum')";

        if ($con->query($sql) === TRUE) {
            echo "New record created successfully";
        } 
        else {
            echo "Error: " . $sql . "<br>" . $con->error;
        }

$con->close();
    }
?>