Need help with form and database

[Andy]

I am slowly learning PHP and right now I stuck on how to verify if a record exists in a table.

I currently have a succesfull connection to my database, now I want to tell it to check a table for a user id, which I have as a variable on the page, and if there is no matching ID in the table show a form empty so it can be filled out.

If there is a matching ID then show the form filled out with the data from the record so it can be updated if the user wants to update it.

Any help would be greatly appreciated. This is by far the largest project I have attempted in PHP.