PHP function not validating

HI
I have this function that doesn't validate user input as required; and inserts values into tables. i.e

function ur() {
if(empty($_POST['a'])) {
if(!eregi('[a-z]', $_POST['a']) {
print "error";
}
}
call to database insert statement made here
}
on the main form

if(!isset($submit)) {

ur();
}

You have a previous thread on this topic. It has been moved from the incorrect snippets forum to the correct forum.