How to use group by in magento collection with join query

Question

In module's admin grid I am using this code to get collection and group them by customer id

$collection = Mage::getModel('referafriend/statistics')->getCollection();
$collection->getSelect()->group('entity_id');
$this->setCollection($collection);

but here i have to use renderer and filter functions for customer info like name and email against each entity_id. i want to join customer model with my module's table. for this i have written this code

 $collection = Mage::getModel('customer/customer')->getCollection()
 ->addNameToSelect();
$collection->getSelect()->join(array('refer' => 'table_name'),'refer.entity_id = e.entity_id'
          ); 
   $collection->getSelect()->group('entity_id'); 
   $collection->addAttributeToSelect('*');

but it gives me this error

SQLSTATE[23000]: Integrity constraint violation: 1052 Column 'entity_id' in group statement is ambiguous

any help will be highly appreciated.

Answer 1

You need to add table name in group by condition.As you did not added on conditions table name at table group('entity_id') so query did not find columns name

 getSelect()->group('e.entity_id');

Logic is:

$collection->getSelect()->group('TABLE_NAME.FIELD_NAME')