added missing use statement to fix #8572

- added unit tests for timestamp behavior and insert with expression
- fixed issue #8572

close #8596

framework/db/mysql/QueryBuilder.php

@@ -7,8 +7,9 @@
 
 namespace yii\db\mysql;
 
-use yii\db\Exception;
 use yii\base\InvalidParamException;
+use yii\db\Exception;
+use yii\db\Expression;
 
 /**
  * QueryBuilder is the query builder for MySQL databases.

framework/db/oci/QueryBuilder.php

@@ -10,6 +10,7 @@ namespace yii\db\oci;
 use yii\base\InvalidParamException;
 use yii\db\Connection;
 use yii\db\Exception;
+use yii\db\Expression;
 
 /**
  * QueryBuilder is the query builder for Oracle databases.