diff --git a/12-dev-guide/12-4-2-data-select-multi-table.md b/12-dev-guide/12-4-2-data-select-multi-table.md
index c4141d51d9b9d52ec058f2aa96be26aa3c1a7ae8..0f4f4234d125bac67fe04199a4468ac1b98c5990 100644
--- a/12-dev-guide/12-4-2-data-select-multi-table.md
+++ b/12-dev-guide/12-4-2-data-select-multi-table.md
@@ -173,7 +173,7 @@ FROM country
 ### 左外连接排除B部分
 若要排除B部分，则在WHRER语句中添加`IS NULL`条件，如下：
 ```sql
-SELECT * FROM A LEFT JOIN B ON A.key = B.key WHRER IS NULL;
+SELECT * FROM A LEFT JOIN B ON A.key = B.key WHRER B.key IS NULL;
 ```
 例如查询没有对应国家的城市
 ```sql
@@ -270,7 +270,7 @@ LIMIT 5;
 ### 右外连接排除A部分
 若要排除A部分，则在WHRER语句中添加`IS NULL`条件，如下：
 ```sql
-SELECT * FROM A RIGHT JOIN B ON A.key = B.key WHRER IS NULL;
+SELECT * FROM A RIGHT JOIN B ON A.key = B.key WHRER A.key IS NULL;
 ```
 例如查询没有对应城市的国家
 ```sql