PHP and MYSQL Query

Guys n Gals,

I need some help with some PHP and MYSQL. I’m not sure how basic / hard it is to do what I am requesting so bare with me here!

Essentially, I have made a form, which the user inputs data into. This data is then stored in the table assigned. When submitting the data, I need the database to query whether certain values that have been inputted are already in the table. It needs to store the data into the table and if there is a duplicate value in the database, it needs to alert the user rather than just go to the success page.

Make any sense? I hope so.

I do not have a clue what commands I need to use to have this happen though. Any help would be much appreciated.

Cheers
Gareth