bug fixed for exercises

data/2.MySQL中阶/4.聚合和分组/2. 求和/sum.md

@@ -34,23 +34,17 @@ select sum(total) from orders where deal and unit_price > 1000;
 
 ### A
 
-```sql
-select sum(total) from orders where deal and unit_price > 1000;
-```
-
-### B
-
 ```sql
 select sum(total) from orders having deal and unit_price > 1000;
 ```
 
-### C
+### B
 
 ```sql
 select sum(total) from orders group by deal having unit_price > 1000;
 ```
 
-### D
+### C
 
 ```sql
 select sum(total) from orders having deal and unit_price > 1000;

data/2.MySQL中阶/4.聚合和分组/3.最小值/min.md

@@ -38,17 +38,11 @@ select dept, min(salary) from employee;
 ### B
 
 ```sql
-select dept, min(salary) from employee;
+select dept, min(salary) from employee order by dept;
 ```
 
 ### C
 
-```sql
-select dept, min(salary) from employee;
-```
-
-### D
-
 ```sql
 select dept, min(total) from employee;
 ```
\ No newline at end of file

data/2.MySQL中阶/4.聚合和分组/5. 平均值/avg.md

@@ -38,17 +38,11 @@ select dept, avg(salary) from employee;
 ### B
 
 ```sql
-select dept, avg(salary) from employee;
+select dept, avg(dept) from employee group by dept;
 ```
 
 ### C
 
 ```sql
-select dept, avg(salary) from employee;
-```
-
-### D
-
-```sql
-select dept, avg(salary) from employee ;
+select dept, avg(salary) from employee group by salary;
 ```

data/2.MySQL中阶/7. 索引/2.创建索引/create_index.md

@@ -41,7 +41,7 @@ create unique index idx_goods_category on goods(category_id);
 ### B
 
 ```sql
-create index idx_goods_category on goods(category_id);
+create index idx_goods_category on goods(name);
 ```
 
 ### C