在关系数据库中，如何从其他表中获取最后一个插入ID

Question

I have two tables that are relational, how do I get the last id of say the first table and use it in another table. I want the $welfare_id variable get the last_insert_id of the first table (another table).

Here is the code:

<?php
include_once('config.php');

if (isset($_POST['record'])) {
    $payeeName = $_POST['payeeName'];
    $amount = $_POST['amount'];
    $welfare_id = LAST_INSERT_ID();

    $myd = $pdo->prepare('INSERT INTO welfare_funeral_payees(Name, Amount, welfare_id)VALUES(:upayeeName, :uamount, :uwelfare_id)');
    $myd->bindParam(':upayeeName', $payeeName);
    $myd->bindParam(':uamount', $amount);
    $myd->bindParam(':uwelfare_id', $welfare_id);


    if ($myd->execute()) {
        ?>
        <script>
            alert("New Welfare created");
        </script>
        <?php
    } else {
        ?>
        <script>
            alert("Couln't not create Welfare");
        </script>
        <?php
    }
}
?>

Answer 1

you have to consider that LAST_INSERT_ID() work on a per-connection base, so, as stated in mysql manual:

The ID that was generated is maintained in the server on a per-connection basis. This means that the value returned by the function to a given client is the first AUTO_INCREMENT value generated for most recent statement affecting an AUTO_INCREMENT column by that client. This value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own. This behavior ensures that each client can retrieve its own ID without concern for the activity of other clients, and without the need for locks or transactions.

this means that you can meaningfully call LAST_INSERT_ID() only after an insert and that id is relevant only for that particular client.

To solve your problem you have to ways: use MAX (as suggested by Nic3500), which has the problem that you are not sure of which id you are really using, or pass the id you need in your post, retrieving in some way before the post (for instance, from a list of already created "welfare")