Fixes #2848: Individual queries should be enclosed within parenthesis in a UNION query

framework/CHANGELOG.md

@@ -61,6 +61,7 @@ Yii Framework 2 Change Log
 - Bug #2740: Fixed the issue that `CaptchaAction::run()` was using obsolete `Controller::createUrl()` method (tonydspaniard)
 - Bug #2760: Fixed GridView `filterUrl` parameters (qiangxue, AlexGx)
 - Bug #2834: When overriding i18n translation sources from config using `app*` or `yii*` default `app` and `yii` sources were not removed (samdark)
+- Bug #2848: Individual queries should be enclosed within parenthesis in a UNION query (qiangxue)
 - Bug: Fixed `Call to a member function registerAssetFiles() on a non-object` in case of wrong `sourcePath` for an asset bundle (samdark)
 - Bug: Fixed incorrect event name for `yii\jui\Spinner` (samdark)
 - Bug: Json::encode() did not handle objects that implement JsonSerializable interface correctly (cebe)

framework/db/QueryBuilder.php

@@ -87,10 +87,16 @@ class QueryBuilder extends \yii\base\Object
             $this->buildHaving($query->having, $params),
             $this->buildOrderBy($query->orderBy),
             $this->buildLimit($query->limit, $query->offset),
-            $this->buildUnion($query->union, $params),
         ];
 
-        return [implode($this->separator, array_filter($clauses)), $params];
+        $sql = implode($this->separator, array_filter($clauses));
+
+        $union = $this->buildUnion($query->union, $params);
+        if ($union !== '') {
+            $sql = "($sql){$this->separator}$union";
+        }
+
+        return [$sql, $params];
     }
 
     /**

framework/db/oci/QueryBuilder.php

@@ -40,9 +40,9 @@ class QueryBuilder extends \yii\db\QueryBuilder
 
         $this->sql = $this->buildLimit($query->limit, $query->offset);
 
-        $unions = $this->buildUnion($query->union, $params);
-        if ($unions !== '') {
-            $this->sql .= $this->separator . $unions;
+        $union = $this->buildUnion($query->union, $params);
+        if ($union !== '') {
+            $this->sql = "{$this->sql}{$this->separator}$union";
         }
 
         return [$this->sql, $params];