These are questions that are frequently asked on the PHP mailing lists, along with compiled versions of all the answers.

1. After I POST data using a form, I hit the back button on my browser and I get a message saying that the data or page has expired! How can I avoid this message, and why does it happen?
   
   
2. I have just inserted a mySQL record with an auto-incrementing field. How do I find out the new number?
   
   
3. I have a <SELECT> tag with a MULTIPLE attribute so I can select multiple options. However, if I submit the form, I don't get all of the options I selected! (I don't want to use Javascript in my forms, either)
   
   
4. I have a database of menu items that I want to sort hierarchially. How can I make sure they are sorted correctly?
   
   
5. I want a quick way to do date arithmetic (Current timestamp - 3 days), but I'm not sure how...