insert array from input to MySQL PDO - php

Question

I tried to insert multiple rows to PDO MySQL but it's didn't work
my code is below
<input type="text" name="firstname[]"> <input type="text" name="lastname[]">
function input_checker($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
$firstname = input_checker($_POST["firstname"]);
$lastname = input_checker($_POST["lastname"]);
$rows = array($firstname, $lastname);
$stmt = $conn->prepare("INSERT INTO memo(ID, firstname, lastname)
VALUES (NULL, :firstname, :lastname)");
foreach($rows as $key => $value){
$stmt->bindParam($key, $value);
}
$stmt -> execute();

Answer 1

$rows is not an associative array, so there's no :firstname and :lastname keys in it. Also, bindParam() binds to references, so using the same $value variable each time through the loop will bind both parameters to the last value from the loop.
You don't need the array in the first place. Just bind each parameter separately.
But $_POST['firstname'] and $_POST['lastname'] are arrays, so you need to loop through them.
$firstname = $lastname = null;
$stmt = $conn->prepare("INSERT INTO memo(ID, firstname, lastname)
VALUES (NULL, :firstname, :lastname)");
$stmt->bindParam(":firstname", $firstname);
$stmt->bindParam(":lastname", $lastname);
foreach ($_POST['firstname'] as $i => $firstname) {
$lastname = $_POST['lastname'][$i];
$stmt->execute();
}

Answer 2

You are binding with the array index as the key (which are numeric in the version you are using), but you are using names for the parameters.
There is no need to use an array anyway as it is shorter to bind each parameter at a time...
$stmt = $conn->prepare("INSERT INTO memo(ID, firstname, lastname)
VALUES (NULL, :firstname, :lastname)");
$stmt->bindParam(":firstname", $firstname);
$stmt->bindParam(":lastname", $lastname);
$stmt -> execute();