sorting not working magento 2

Question

I created a custom column "product_name" in sales/order grid,

When I am sorting this column grid showing error:

Item (Magento\Framework\View\Element\UiComponent\DataProvider\Document) with the same id "146" already exist

My collection code is :

 parent::_initSelect();
        $joinTable = $this->getTable('mg_dispatch_date');
        $joinTable2 =$this->getTable('customer_entity_varchar');
        $joinTable3 = $this->getTable('catalog_product_entity_varchar');
        $this->getSelect()->join($joinTable . ' as mdd', 'main_table.entity_id = mdd.order_id', array('*')); 
        $this->getSelect()->join($joinTable2. ' as fn', 'main_table.customer_id = fn.entity_id and fn.attribute_id = 177',array('value'));
       $this->getSelect()->join($joinTable3.' as cpev','main_table.entity_id = cpev.entity_id', array('*'));  
        return $this;

and sales_order_item.xml code is :

<column name="product_name" class="Magecoder\Customerref\Ui\Component\Listing\Column\Productname">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">

            <item name="filter" xsi:type="boolean">false</item>
            <item name="sortable" xsi:type="boolean">true</item>
                    <item name="bodyTmpl" xsi:type="string">ui/grid/cells/html</item>
                    <item name="visible" xsi:type="boolean">true</item> 
                    <item name="label" xsi:type="string" translate="true">Product Name</item>
                </item>
            </argument>
        </column>

Please help is anyone have suggestion, Thanks in Advance.

Answer 1

There are not the filters by product attribute_id and store_id in the query. It is the reason for result has several rows for each product.

Also, the order can be contains many products - you can use GROUP_CONCAT for compose all product name in one row for each order.

If you don't want to show all order's products for the order row you can add

$this->getSelect()->group('main_table.entity_id');