Correct way to process data with LOCK TABLES

[new7media]

I need to get the auto-increment value of the last inserted record to use later in a script. I'm just wondering which is the better way to write the code below that would lock the table that will provide the auto-increment info. Or does it matter if I do the mysql_insert_id() inside or outside of the table locking?

mysql_query("LOCK TABLES tablename READ/WRITE");
mysql_query(INSERT INTO tablename (id,content) VALUES (NULL,'$content')";
$id = mysql_insert_id();
mysql_query("UNLOCK TABLES");
...rest of script

OR

mysql_query("LOCK TABLES tablename READ/WRITE");
mysql_query(INSERT INTO tablename (id,content) VALUES (NULL,'$content')";
mysql_query("UNLOCK TABLES");
$id = mysql_insert_id();
...rest of script

[Roger_Ramjet]

mysql_insert_id works on a per connection basis so if you run it straight after an insert it will return the id from the current session even if you are not table locked and another session inserts a row imediately after yours. Read the user notes for some pointers and tips, and there are a few ways to get this info besides insert id.