<?php
  $species = $_POST['species'];
  $name = $_POST['name'];
  $owner = $_POST['owner'];
  $dob = $_POST['dob'];

  // INSERT VALIDATION AND ERROR CHECKING CODE HERE

  $db = new SQLite3('pet.db');  // open the DB

  // check that primary key 'name' doesn't already exist in db
  $query = "SELECT name FROM pet WHERE name='" . $name . "'";
  $result = $db->query($query);
  if ($result->fetchArray()[0] != null) {
     // pet name already in database
     $db->close();
     require('pet.php');
     return;
  }

  $command = "INSERT INTO pet VALUES('" . $species  . "', '" . $name . 
      "', '" . $owner . "', '" . $dob . "')";
  $result = $db->exec($command); // execute the command
  if ($result) {
     require('pet.php');
  }
  $db->close();
?>