MAGETWO-56676: Product rule fix

Author: slopukhov

app/code/Magento/Rule/Model/Condition/Product/AbstractProduct.php

@@ -602,7 +602,9 @@ public function getBindArgumentValue()
      */
     public function getMappedSqlField()
     {
-        if (!$this->isAttributeSetOrCategory()) {
+        if ($this->getAttribute() == 'sku') {
+            $mappedSqlField = 'e.sku';
+        } elseif (!$this->isAttributeSetOrCategory()) {
             $mappedSqlField = $this->getEavAttributeTableAlias() . '.value';
         } elseif ($this->getAttribute() == 'category_ids') {
             $mappedSqlField = 'e.entity_id';