If you’re anything like me, you generally set up an auto-incrementing integer field in most of your MySQL tables that can be used as the primary key for your records. A lot of times, after inserting new information into the database, you need a way to find out what ID was assigned to your data when you created the new row. With MySQL, it’s really simple to get that information. MySQL offers a function called “LAST_INSERT_ID” that does just that.
As soon as you finish inserting the new row, if you run another SQL query that looks like “SELECT LAST_INSERT_ID()” on your database, the result you get back will be the most recently added auto-increment number in your MySQL installation.
PHP also has a built-in function to perform this operation. Instead of setting up a separate MySQL query, executing it and retrieving the results from it, you can simply use the mysql_insert_id() function, which will automatically perform those steps and simply return the ID number.