Fix count SQL on products sold collection

app/code/Magento/Reports/Model/ResourceModel/Product/Sold/Collection.php

@@ -11,6 +11,8 @@
  */
 namespace Magento\Reports\Model\ResourceModel\Product\Sold;
 
+use Magento\Framework\DB\Select;
+
 /**
  * @SuppressWarnings(PHPMD.DepthOfInheritance)
  */
@@ -109,6 +111,19 @@ public function setOrder($attribute, $dir = self::SORT_ORDER_DESC)
         return $this;
     }
 
+    /**
+     * @return Select
+     */
+    public function getSelectCountSql()
+    {
+        $countSelect = clone parent::getSelectCountSql();
+
+        $countSelect->reset(Select::COLUMNS);
+        $countSelect->columns('COUNT(DISTINCT order_items.item_id)');
+
+        return $countSelect;
+    }
+
     /**
      * Prepare between sql
      *

app/code/Magento/Reports/Test/Unit/Model/ResourceModel/Product/Sold/Collection/CollectionTest.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace Magento\Reports\Test\Unit\Model\ResourceModel\Product\Sold\Collection;
+
+use Magento\Framework\DB\Select;
+use Magento\Framework\TestFramework\Unit\Helper\ObjectManager;
+use Magento\Reports\Model\ResourceModel\Product\Sold\Collection;
+
+/**
+ * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
+ */
+class CollectionTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @var ObjectManager
+     */
+    protected $objectManager;
+
+    /**
+     * @var \PHPUnit_Framework_MockObject_MockObject
+     */
+    protected $selectMock;
+
+    protected function setUp()
+    {
+        $this->objectManager = new ObjectManager($this);
+        $this->selectMock = $this->getMock(Select::class, [], [], '', false);
+    }
+
+    public function testGetSelectCountSql()
+    {
+        /** @var $collection \PHPUnit_Framework_MockObject_MockObject */
+        $constructArgs = $this->objectManager->getConstructArguments(Collection::class);
+        $collection = $this->getMock(Collection::class, ['getSelect'], $constructArgs, '', false);
+
+        $collection->expects($this->atLeastOnce())->method('getSelect')->willReturn($this->selectMock);
+
+        $this->selectMock->expects($this->atLeastOnce())->method('reset')->willReturnSelf();
+        $this->selectMock->expects($this->exactly(2))->method('columns')->willReturnSelf();
+
+        $this->selectMock->expects($this->at(6))->method('columns')->with('COUNT(DISTINCT main_table.entity_id)');
+
+        $this->selectMock->expects($this->at(7))->method('reset')->with(Select::COLUMNS);
+        $this->selectMock->expects($this->at(8))->method('columns')->with('COUNT(DISTINCT order_items.item_id)');
+
+        $this->assertEquals($this->selectMock, $collection->getSelectCountSql());
+    }
+}