diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 6054b71115..9799339b29 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -82,6 +82,7 @@ Yii Framework 2 Change Log
 - Enh #2051: Do not save null data into database when using RBAC (qiangxue)
 - Enh #2101: Gii is now using model labels when generating search (thiagotalma)
 - Enh #2103: Renamed AccessDeniedHttpException to ForbiddenHttpException, added new commonly used HTTP exception classes (danschmidt5189)
+- Enh #2124: Added support for UNION ALL queries (Ivan Pomortsev, iworker)
 - Enh: Added `favicon.ico` and `robots.txt` to default application templates (samdark)
 - Enh: Added `Widget::autoIdPrefix` to support prefixing automatically generated widget IDs (qiangxue)
 - Enh: Support for file aliases in console command 'message' (omnilight)
diff --git a/framework/db/Query.php b/framework/db/Query.php
index 2039100ed7..9a42009495 100644
--- a/framework/db/Query.php
+++ b/framework/db/Query.php
@@ -635,11 +635,12 @@ class Query extends Component implements QueryInterface
 	/**
 	 * Appends a SQL statement using UNION operator.
 	 * @param string|Query $sql the SQL statement to be appended using UNION
+	 * @param bool $all TRUE if using UNION ALL and FALSE if using UNION
 	 * @return static the query object itself
 	 */
-	public function union($sql)
+	public function union($sql, $all = false)
 	{
-		$this->union[] = $sql;
+		$this->union[] = [ 'query' => $sql, 'all' => $all ];
 		return $this;
 	}
 
diff --git a/framework/db/QueryBuilder.php b/framework/db/QueryBuilder.php
index 7cadc1d6fc..4c51c28cc2 100644
--- a/framework/db/QueryBuilder.php
+++ b/framework/db/QueryBuilder.php
@@ -739,16 +739,23 @@ class QueryBuilder extends \yii\base\Object
 		if (empty($unions)) {
 			return '';
 		}
+		
+		$result = '';
+		
 		foreach ($unions as $i => $union) {
-			if ($union instanceof Query) {
+			$query = $union['query'];
+			if ($query instanceof Query) {
 				// save the original parameters so that we can restore them later to prevent from modifying the query object
-				$originalParams = $union->params;
-				$union->addParams($params);
-				list ($unions[$i], $params) = $this->build($union);
-				$union->params = $originalParams;
+				$originalParams = $query->params;
+				$query->addParams($params);
+				list ($unions[$i]['query'], $params) = $this->build($query);
+				$query->params = $originalParams;
 			}
+			
+			$result .= 'UNION ' . ($union['all'] ? 'ALL ' : '') . '( ' . $unions[$i]['query'] . ' ) ';
 		}
-		return "UNION (\n" . implode("\n) UNION (\n", $unions) . "\n)";
+		
+		return trim($result);
 	}
 
 	/**
diff --git a/tests/unit/framework/db/QueryBuilderTest.php b/tests/unit/framework/db/QueryBuilderTest.php
index 3e18bb6136..d9f9960920 100644
--- a/tests/unit/framework/db/QueryBuilderTest.php
+++ b/tests/unit/framework/db/QueryBuilderTest.php
@@ -215,4 +215,30 @@ class QueryBuilderTest extends DatabaseTestCase
 		$this->assertEquals($expectedQueryParams, $queryParams);
 	}
 	*/
+	
+	/*
+	This test contains three select queries connected with UNION and UNION ALL constructions.
+	It could be useful to use "phpunit --group=db --filter testBuildUnion" command for run it.
+	
+	 public function testBuildUnion()
+	 {
+	 	$expectedQuerySql = "SELECT `id` FROM `TotalExample` `t1` WHERE (w > 0) AND (x < 2) UNION ( SELECT `id` FROM `TotalTotalExample` `t2` WHERE w > 5 ) UNION ALL ( SELECT `id` FROM `TotalTotalExample` `t3` WHERE w = 3 )";
+    		$query = new Query();
+    		$secondQuery = new Query();
+    		$secondQuery->select('id')
+      			->from('TotalTotalExample t2')
+      			->where('w > 5');
+    		$thirdQuery = new Query();
+    		$thirdQuery->select('id')
+      			->from('TotalTotalExample t3')
+      			->where('w = 3');
+    		$query->select('id')
+      			->from('TotalExample t1')
+      			->where(['and', 'w > 0', 'x < 2'])
+      			->union($secondQuery)
+      			->union($thirdQuery, TRUE);
+    		list($actualQuerySql, $queryParams) = $this->getQueryBuilder()->build($query);
+    		$this->assertEquals($expectedQuerySql, $actualQuerySql);
+  	 }*/
+
 }