Filter results from a serialized string to use on statistics

So basically the form saves a large serialized array in the database. Now since you have multiple forms, you need to iterate over the result from get_results, unserialize the column and then access the city key.

global $wpdb;
$table_name = $wpdb->prefix.'db7_forms';
$results = $wpdb->get_results( "SELECT form_value FROM $table_name WHERE form_post_id = 6062", OBJECT );
// iterate over results
foreach ($results as $result) {
    $data = unserialize($result->form_value);
    // now the city is in $data['city']
}