Magento distinct(true) clause ignored

Question

Using the following code:

$collection = Mage::getModel('custom/custom')
    ->getCollection()
    ->distinct(true)
    ->addFieldToSelect('brand')
    ->load();

I've found the distinct is being ignored in 1.4.2, exactly the same code in 1.8.1 is working as I would expect (returning a single entry for each brand).

1.4.2 result:

"Ace"
"Ace"

1.8.1 result:

"Ace"

For myself I notice that 1.4.2 is returning an array of all fields from the model for each object , rather than just the one specified in the select (brand) as 1.8.1 does. I think this is what's causing the problem the distinct is included in the SELECT on both versions - in fact the SELECT statements are identical across versions.

Is there a way to get a distinct result for a single field in older versions of Magento?

EDIT

Based on the discussion below with liyakat my final solution was:

$collection = Mage::getModel('custom/custom')
    ->getCollection()
    ->distinct(true)
    ->addFieldToSelect('brand')
    ->setOrder('brand', 'ASC');

$collection->getSelect()->group('brand');
$collection->load();

Answer 1

you can add this function to get select statement of collection. and i am sure you will get result.

   $collection = Mage::getModel('custom/custom')
        ->getCollection()    
        ->addFieldToSelect('brand')
        ->load();

   $collection->getSelect()->columns(
    array('asbrand' => new Zend_Db_Expr(
        "distinct(brand)")
        )
    );

hope this will work for you.