fixed mistake question

data/3.MySQL高阶/1.深入索引/4.组合索引/combinate.md

@@ -27,7 +27,7 @@ Joe 应该如何优化？
 ## 答案
 
 ```sql
-alter table goods add index (`stock-id`, category_id, name);
+alter table goods add index (stock, category_id, name);
 ```
 
 ## 选项
@@ -35,7 +35,7 @@ alter table goods add index (`stock-id`, category_id, name);
 ### A
 
 ```sql
-alter table goods add index (`stock-id` and category_id and name);
+alter table goods add index (stock and category_id and name);
 ```
 
 ### B
@@ -47,5 +47,5 @@ alter table goods add index (concat(stock, category_id, name));
 ### C
 
 ```sql
-alter table goods add index (`stock-id` + category_id + name);
+alter table goods add index (stock + category_id + name);
 ```