need a better method for a snippet in php

Question

Hi!

Say I have a database called Poll and have these two table structures. poll table has fields pid (auto_inc) and title. choices table has cid (auto_inc), pid, and text.

How do i add a value to the poll table and at the same time get the pid of the most recent entry in the poll table to be used as the pid in the choices table? So far I have this:

<?php
$sql = "INSERT INTO poll (pid, title) VALUES (NULL, 'sometitle')";
if (mysql_query($sql)) {
  // get the latest pid
  $pid = mysql_result(mysql_query("SELECT pid FROM poll ORDER BY pid DESC LIMIT 1"), 0);

  // use the latest pid retrieved to insert to the "choices" table
  $sql = "INSERT INTO choices (cid, pid, text) VALUES (NULL, " . $pid . ", 'sometext')";
  mysql_query($sql);
}
?>

I just have a feeling that there's a better solution to this.

Thanks!

Answer 1

There are two ways of doing this:

Firstly the PHP function mysql_insert_id(). (See http://www.php.net/mysql_insert_id). This will return the last auto_increment ID inserted.

This doesn't handle large numbers very well, although in practice it ought not to be an issue. The second way (and my preferred way) is to run this query:

Select LAST_INSERT_ID() As insert_id

Make sure to call this before you run any other queries - it must be called directly after the query that does the insert. (See the php.net page above for more info, etc)

The current way you're doing it also suffers from concurrency issues: if somebody else is inserting a poll at the same time, you run the risk of the pids being mixed up.