Please use this code

$productCollection = Mage::getResourceModel('catalog/product_collection')

                        ->joinField('category_id', 'catalog/category_product', 'category_id', 'product_id=entity_id', null, 'left')
                        ->addAttributeToFilter('category_id', 3);
                       $productCollection->getSelect()->group('product_id')->distinct(true);
echo '<pre>'; print_r($productCollection->getData());

Definitely this work for you.

Product Collection from Category

// Step 1
$category = Mage::getModel('catalog/category')->load($category_id);

// Step 2
$productCollection = Mage::getModel('catalog/product')->getCollection();

// Step 3
$productCollection->addCategoryFilter($category);

// Step 4
$productCollection
    ->addAttributeToSelect('sku')
    ->addAttributeToSelect('another_attribute')
    ->addAttributeToFilter('type_id', 'simple')
    ->addAttributeToFilter('status', 1);

// Now you can loop through your collection
foreach($productCollection as $product) {
    $product->getSku();
    $product->getAnotherAttribute();
    // and so on...
}

So what's going on?

1. We loaded a category model. We will use that in the product collection.
2. We instantiated the product collection model.
3. We added the category for filtering.
4. We added the appropriate attributes for selection and filtering.

NOTE: Do not use the asterisk unless you plan on using every attribute being returned. Just like you shouldn't use the asterisk in a MySQL query unless you plan on getting everything from that table.

Once I have all my attributes and filters in place, I can loop through my collection. I do not need to call the load() method because lazy loading does that for me.

Once I'm in the loop, I have access to the product object Mage_Catalog_Model_Product. I do not need to instantiate another model inside the loop. The collection does this for me.