来自mySQL的下拉列表中的重复条目

Okay so I'm new to mySQL. I'm sorry this is a very novice question. Essentially I have two tables, Associates, and keys.
The content is as follows:

associates: id, department, associate, date_added

keys: id, key_name, date_added,

my code to make my dropdown is as follows:

<?php
mysql_connect('hostname', 'user', 'Password');
mysql_select_db('log');

$key_fetch = "SELECT `associates`.`department`,`associates`.`associate`,`keys`.`key_name` FROM associates , `keys` ORDER BY `key_name` DESC";
$results = mysql_query($key_fetch);

echo "<select name='key_name' size='5'>";
while ($row = mysql_fetch_array($results)) {
echo "<option value='" . $row['key_name'] . "'>" . $row['key_name'] . "</option>";
}
echo "</select>";
?>

The problem is I only have 5 keys and I have ten associates, and this creates duplicates in my dropdown and I can't fix it with SELECT DISTINCT, and I'm not too sure what else to try.

To visualize cartesian product based on above Q comments.

create table t1
(   id int auto_increment primary key,
    stuff1 varchar(50) not null
);
insert t1 (stuff1) values ('111.1'),('111.2'),('111.3');

create table t2
(   id int auto_increment primary key,
    stuff2 varchar(50) not null
);
insert t2 (stuff2) values ('222.1'),('222.2'),('222.3');

A: an explicit Join

select t1.id,t1.stuff1,t2.stuff2 
from t1 
join t2 
on t2.id=t1.id;
+----+--------+--------+
| id | stuff1 | stuff2 |
+----+--------+--------+
|  1 | 111.1  | 222.1  |
|  2 | 111.2  | 222.2  |
|  3 | 111.3  | 222.3  |
+----+--------+--------+

B: An old-style cartesian product

select t1.id,t1.stuff1,t2.stuff2 
from t1,t2;
+----+--------+--------+
| id | stuff1 | stuff2 |
+----+--------+--------+
|  1 | 111.1  | 222.1  |
|  2 | 111.2  | 222.1  |
|  3 | 111.3  | 222.1  |
|  1 | 111.1  | 222.2  |
|  2 | 111.2  | 222.2  |
|  3 | 111.3  | 222.2  |
|  1 | 111.1  | 222.3  |
|  2 | 111.2  | 222.3  |
|  3 | 111.3  | 222.3  |
+----+--------+--------+
9 rows in set (0.00 sec)

C: Cross join, same output as B:

select t1.id,t1.stuff1,t2.stuff2 
from t1 cross join t2

So, your output, as I see it, is like B, 50 rows.