How can get unique values from data table using dql?

I am having a table in which there is a column in which various values are stored.i want to retrieve unique values from that table using dql.

         Doctrine_Query::create()
                    ->select('rec.school')
                    ->from('Records rec')                   
                    ->where("rec.city='$city' ")                                    
                    ->execute();        

Now i want only unique values. Can anybody tell me how to do that…

Edit

Table Structure:

CREATE TABLE IF NOT EXISTS `records` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`state` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
 `city` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
 `school` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
 PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=16334 ;

This is the Query I am using:

   Doctrine_Query::create()
          ->select('DISTINCT rec.city')
          ->from('Records rec')                   
          ->where("rec.state = '$state'")                                    
             // ->getSql();
           ->execute();                 

Generting Sql for this gives me:

SELECT DISTINCT r.id AS r__id, r.city AS r__city FROM records r WHERE r.state = 'AR'

Now check the sql generated:::: DISTINCT is on ‘id’ column where as i want Distinct on city column. Anybody know how to fix this.

EDIT2

Id is unique cause its an auto incremental value.Ya i have some real duplicates in city column like: Delhi and Delhi. Right.. Now when i am trying to fetch data from it, I am getting Delhi two times. How can i make query like this:

  select DISTINCT rec.city where state="xyz";

Cause this will give me the proper output.

EDIT3:

Anybody who can tell me how to figure out this query..???

Answer

Depends on what version you are using, but I had the same issue and ->distinct() worked for me.

Doctrine_Query::create()
      ->select('rec.city')->distinct()
      ->from('Records rec')                   
      ->where("rec.state = '$state'")                                    
       ->execute();