diff --git a/framework/yii/db/cubrid/Schema.php b/framework/yii/db/cubrid/Schema.php
index c7b6ad2..99624f6 100644
--- a/framework/yii/db/cubrid/Schema.php
+++ b/framework/yii/db/cubrid/Schema.php
@@ -7,7 +7,6 @@
 
 namespace yii\db\cubrid;
 
-use yii\base\NotSupportedException;
 use yii\db\Expression;
 use yii\db\TableSchema;
 use yii\db\ColumnSchema;
diff --git a/framework/yii/db/mssql/Schema.php b/framework/yii/db/mssql/Schema.php
index 5f53d8e..9def3b4 100644
--- a/framework/yii/db/mssql/Schema.php
+++ b/framework/yii/db/mssql/Schema.php
@@ -7,7 +7,6 @@
 
 namespace yii\db\mssql;
 
-use yii\db\mssql\TableSchema;
 use yii\db\ColumnSchema;
 
 /**
diff --git a/framework/yii/db/mysql/QueryBuilder.php b/framework/yii/db/mysql/QueryBuilder.php
index 1b67cda..386de2f 100644
--- a/framework/yii/db/mysql/QueryBuilder.php
+++ b/framework/yii/db/mysql/QueryBuilder.php
@@ -9,7 +9,6 @@ namespace yii\db\mysql;
 
 use yii\db\Exception;
 use yii\base\InvalidParamException;
-use yii\db\mysql\Schema;
 
 /**
  * QueryBuilder is the query builder for MySQL databases.