Can't send query to db - php

Question

im trying out some code by my own. I just started to learn PHP & mysql. Could anyone tell me where is the mistake? I got a error when processing the query.
My db is set like in the code.
Db name: sweepstakes
Table name: alfa
<?php
$dbhost = "localhost";
$dbuser = "root";
$dbpass = "";
$dbname = "sweepstakes";
$db = mysqli_connect($dbhost,$dbuser,$dbpass, $dbname);
if(mysqli_connect_errno()){
die("Database connection failed: " .
mysqli_connect_errno() .
" (" . mysqli_connect_errno() . ")"
);
}
if($_SERVER['REQUEST_METHOD']=='POST'
&& $_POST['submit']=='Submit'
&& !empty($_POST['name'])
&& !empty($_POST['description'])
&& !empty($_POST['adress'])) {
$name = $_POST['name'];
$desc = $_POST['description'];
$adress = $_POST['adress'];
$query = "INSERT INTO alfa (name, description, adress) VALUES ('$name', '$desc', '$adress')";
$result = mysqli_query($db, $query);
if($result){
}else{
die("Database query failed." . mysql_error() . " " . mysqli_connect_error($db));
}
} else { echo "Empty!";
}
?>
<form method="post" action="index.php">
<fieldset>
<legend>New Sweepstakes</legend>
<label>Name: </br>
<input type="text" name="name" maxlength="150" />
</label> </br>
<label>Description:</br>
<textarea name="description" cols="45" rows="10"></textarea>
</label> </br>
<label>Adress:</br>
<input type="text" name="adress" maxlength="1080" />
</label> </br>
<input type="submit" name="submit" value="Submit" />
</fieldset>
</form>

Answer 1

You're mixing mysql and mysqli functions. Stick with mysqli, mysql is deprecated (don't use it).
In case you didn't spot it: mysql_error() should be mysqli_error()

Answer 2

In addition to checking what Halcyon writes ( using mysqli_error() ), I would also check the query string itself. Just echo out $query right after it's built (the $query = "INSERT..." line) and when running the script look to see if the output matches what you expect to happen, ie that you see something like INSERT INTO alfa (name, description, adress) VALUES ('fred', 'blonde dude', 'Anywhere 32B'). If anything looks out of place (like maybe you have a ' or " in the inputed data and it's screwing up the string output), fix it and try again.
echo and print and print_r()are your friends when doing detective work on new code to see what is the output expected.
(edit)
After reading your update with Halcyon, you should probably check how your auto-incremented field is set up. If, for example, you've been tinkering with this for a while but only set the auto-increment field to INT(2), you might have run out of space for numbers (can only go up to 99 with INT(2)). Increase it to INT(11) or something similar, empty the table, and try again. You can also try ALTER TABLEtable_nameAUTO_INCREMENT = 1 to reset the auto numbering.