WordPress：$ wpdb查询返回double

I have been stuck on this for about an hour and my hair is turning grey.

For some reason when I try to run this query:

$sql = "SELECT * FROM wp_units WHERE user_id = $user->ID AND post_units = $id";
$results = $wpdb->get_results($sql);

foreach ($results as $result) {
  echo $result->post_units;

}

I get this output:

99 1212 1616 1919

In the database I have:

|id | user_id | post_units
 1      1        9
 2      1        12
 3      1        16
 4      1        19

Can anyone see why?

Edit:

$wpdb->last_query; also returns double the times.

SELECT * FROM wp_units WHERE user_id = 1 AND post_units = 9 SELECT * FROM wp_units WHERE user_id = 1 AND post_units = 9