PHP registration script: verifying and telling the user what went wrong

Question

Hi,

I'm building a registration script and I want to insert the user's input (username, mail) ONLY if it's not already in the database. What I usually do in such cases is a request to see if something's already there, something like: "SELECT * FROM things WHERE thing_name = '$treated_user_input'".

I have two fields that need to be unique this time though. Is there a way to do only one SELECT request and still be able to tell the user exactly what field went wrong? Or do I have to do one request per unique field?

Thanks for your answers.

Answer 1

Look at http://stackoverflow.com/questions/192924/sql-distinct-for-2-fields-in-a-database for selecting two distinct fields. At that point, if you have at least one result, you can use PHP to determine which is the offending field.