MySQL Insert Select - mysql

Question

Ran into a bit of trouble when trying to insert records into my DB from my forum
What it does when you create a thread is make an entry into 2 tables. First the forum_threads table with information on the thread title, description, poster, post time, etc. It will use thread_id with AUTO_INTEGER to generate the threads ID.
I then need to get that thread_id from the forum_threads and then put that as the thread_id in the forum_posts table.
I'm not sure if theres anyway I can select a row based on its ID after I just inserted it. Would I just have to select the most recent ID? Would that leave a margin of error? Other thought I had was to select based on user name and post time.
Thoughts?
<?php
if (isset($_POST['submit'])) {
$thread_sql = "
INSERT INTO forum_threads (
user_id,
forum_id,
thread_postdate,
thread_title,
thread_description,
thread_icon
) VALUES (
'$_SESSION[user_id]',
'$_GET[f]',
'$date',
'$_POST[topictitle]',
'$_POST[topicdescription]',
'$_POST[posticon]'
)
";
$thread_query = #mysqli_query ($db_connect, $thread_sql);
$post_sql = "
INSERT INTO forum_posts (
user_id,
thread_id,
post_message,
post_date
) VALUES (
'$_SESSION[user_id]',
'',
'$_POST[content]',
'$date'
)
";
$post_query = #mysqli_query ($db_connect, $post_sql);
}
?>

Answer 1

To first answer your question directly, the function mysql_insert_id() will return the ID that was assigned to the most recently inserted row. There's no guesswork involved; MySQL will happily tell you (through its own built-in LAST_INSERT_ID() function) what ID it assigned.
On a separate note, I see that you're directly inserting values from $_POST into your SQL statement. Never, ever, EVER do that. This exposes your application to SQL injection attacks.
Either use the mysql_real_escape_string() function to properly escape the values for use in a SQL statement, or, since you're already using mysqli_ functions, use placeholders (? values) to create a prepared statement.

Answer 2

MySqli_Insert_Id () will return the last auto generated ID. Call this function immediately after you insert your new thread.

Answer 3

INSERT
INTO forum_threads (…)
VALUES (…)
INSERT
INTO forum_posts (thread_id, …)
VALUES (LAST_INSERT_ID(), …)

Answer 4

You can just use the last_insert_id to get the ID of the row you just inserted; don't worry about anybody else inserting a row just after, the last_insert_id is per-connection, so unless they used your connection, you're safe.
There is an API-level call to retrieve this so you don't need to ask the server specifically.
Oh yes, also, do not use the # operator in PHP, ever, google for it if you want to know why it's bad.

Answer 5

Use MySQL's last_insert_id() function in sql code or the php wrapper for it mysql_insert_id() in a php script. These will give you the last auto_increment number generated in your connection. So it's thread safe.