Mysqli_query dont insert details to table - php

Question

My function, need to check i the email in use. if the email not registered yet.
the code will check if the username at use. if its not registered before.
its need to start the proccesing of the INSERT Mysqli_query.
than the problem starts, its not show any prob & its check the email & username rightly,
only the mysqli_query command, doesn't work.
1)Why its not work?
2)How to make it more secure?
My code:
if(empty($error)){
$sqlcon = mysqli_connect("localhost","baruch","","developers");
$checkemail = mysqli_query($sqlcon,"SELECT `email` FROM `users` WHERE email='$email'");
if(mysqli_num_rows($checkemail)){echo "האימייל".$email.".בשימוש בחרו באימייל אחר.";}else{
$checkusername = mysqli_query($sqlcon,"SELECT `username` FROM `users` WHERE username='$username'");
if(mysqli_num_rows($checkusername)){echo "שם המשתמש: <strong>".$username."</strong> ,נמצא בשימוש ביחרו שם משתמש אחר.";}else{
mysqli_query($sqlcon, "INSERT INTO `users` (`ID`, `fullname`, `username`, `password`, `email`, `birthday`, `tags`, `gold`, `activation`, `avatarurl`) VALUES ('', '$fullname', '$username', MD5('$password'), '$email', '$birthday', '$tags', '0', '0', MD5('".rand()."'), '')");
echo $fullname." נרשמת בהצלחה לאתר, בשם המשתמש:".$username;
}
}
mysqli_close($sqlcon);
}

Answer 1

You have column mismatch error,
Try this,
mysqli_query($sqlcon, "INSERT INTO `users` (`ID`, `fullname`, `username`, `password`, `email`, `birthday`, `tags`, `gold`, `activation`, `avatarurl`)
VALUES ('', '$fullname', '$username', MD5('$password'), '$email', '$birthday', '$tags', '0', '0', '')");

Answer 2

mysqli_real_escape_string() all these $variables: ('', '$fullname', '$username', MD5('$password'), '$email', '$birthday', '$tags', '0', '0', MD5('".rand()."'), '').
Like: $fullname = mysqli_real_escape_string($connection, $fullname); and such...
Or use a prepared statement to take care of things for you.