journalism

I have some online form and right now I have seen some small problem.

1. Some of the data are being duplicate the same data.
Q. What is the html or php or script to use so that it can be automatically check if the data is already use (i.e. username or email)?

2. Some of the form are blank no data has been entered.
Q. What is the html or php or script to use so that the single form or a text field can be required to fill in some data on it?


Thanks in advance.