How to use Distinct in magento1?

Question

I want to use distinct in magento.

SELECT DISTINCT level FROM `student`

I am trying this code

 $collection = Mage::getModel('school/student')->getCollection()
      ->distinct(true)
      ->addAttributeToSelect('level');

But its not working.

So how to use distinct in magento

Answer 1

Use group by instead of distinct.

Add $collection->getSelect()->group('level').

Use group by instead of ->distinct(true).

Code:

$collection = Mage::getModel('school/student')->getCollection()
          ->addFieldToSelect('level');

$collection->getSelect()->group('level')

Or use:

$collection = Mage::getModel('school/student')->getCollection()->getSelect()
      ->columns('level')
      ->group('level');

Answer 2

Tested on Magento ver 1.9.4.3.

$collection = Mage::getResourceModel('sales/order_collection')
    ->addFieldToSelect('customer_id')
    ->distinct(true)
    ->addFieldToFilter('entity_id', ['gteq' => 200737]);

The resulting MySQL statement is:

SELECT DISTINCT `main_table`.`customer_id` 
FROM `sales_flat_order` AS `main_table` 
WHERE (main_table.entity_id >= 200737)

To return a one-dimension array of customer_id, do:

$result = $collection->getColumnValues('customer_id');