MAGETWO-39957: Catalog Price Rule does not apply to Group price

Author: Roman Ganin

app/code/Magento/Catalog/Model/Product/Attribute/Backend/GroupPrice/AbstractGroupPrice.php

@@ -432,4 +432,14 @@ public function getAffectedFields($object)
 
         return $data;
     }
+
+    /**
+     * Get resource model instance
+     *
+     * @return \Magento\Catalog\Model\Resource\Product\Attribute\Backend\GroupPrice
+     */
+    public function getResource()
+    {
+        return $this->_getResource();
+    }
 }

app/code/Magento/CatalogRule/Model/Indexer/IndexBuilder.php

@@ -82,6 +82,11 @@ class IndexBuilder
      */
     protected $batchCount;
 
+    /**
+     * @var \Magento\Catalog\Model\Product
+     */
+    protected $product;
+
     /**
      * @param RuleCollectionFactory $ruleCollectionFactory
      * @param PriceCurrencyInterface $priceCurrency
@@ -612,6 +617,17 @@ protected function getRuleProductsStmt($websiteId, $productId = null)
             $select->where('rp.product_id=?', $productId);
         }
 
+        /**
+         * Join group price to result
+         */
+        $groupPriceAttr = $this->eavConfig->getAttribute(Product::ENTITY, 'group_price');
+        $select->joinLeft(
+            ['gp' => $groupPriceAttr->getBackend()->getResource()->getMainTable()],
+            'gp.entity_id=rp.product_id AND gp.customer_group_id=rp.customer_group_id AND '
+            . $this->getReadAdapter()->getCheckSql('gp.website_id=0', 'TRUE', 'gp.website_id=rp.website_id'),
+            'value'
+        );
+
         /**
          * Join default price and websites prices to result
          */
@@ -653,7 +669,10 @@ protected function getRuleProductsStmt($websiteId, $productId = null)
             []
         );
         $select->columns([
-            'default_price' => $this->getReadAdapter()->getIfNullSql($tableAlias . '.value', 'pp_default.value'),
+            'default_price' => $this->getReadAdapter()->getIfNullSql(
+                    'gp.value',
+                    $this->getReadAdapter()->getIfNullSql($tableAlias . '.value', 'pp_default.value')
+                ),
         ]);
 
         return $read->query($select);