Have a look at the method `Mage_Core_Model_Resource_Db_Collection_Abstract::addExpressionFieldToSelect()`:

    /**
     * Add attribute expression (SUM, COUNT, etc)
     * Example: ('sub_total', 'SUM({{attribute}})', 'revenue')
     * Example: ('sub_total', 'SUM({{revenue}})', 'revenue')
     * For some functions like SUM use groupByAttribute.
     *
     * @param string $alias
     * @param string $expression
     * @param array $fields
     * @return Mage_Core_Model_Resource_Db_Collection_Abstract
     */
    public function addExpressionFieldToSelect($alias, $expression, $fields)
    {
        // validate alias
        if (!is_array($fields)) {
            $fields = array($fields=>$fields);
        }

        $fullExpression = $expression;
        foreach ($fields as $fieldKey=>$fieldItem) {
            $fullExpression = str_replace('{{' . $fieldKey . '}}', $fieldItem, $fullExpression);
        }

        $this->getSelect()->columns(array($alias=>$fullExpression));

        return $this;
    }

Usage
----

    $collection->addExpressionFieldToSelect("page_view", "sum({{page_view}})", ["page_view"]);
    //                                      ^ alias      ^ expression          ^ used fields

    $collection->getSelect()->group("page_view");