fixed a typo

data/2.MySQL中阶/5.子查询/4.EXISTS/exists.md

@@ -24,12 +24,12 @@ create table employee(
 ## 答案
 
 ```sql
-select id, name, dept
+select id, name, dept_id
 from employee as o
 where not exists(
     select * 
     from employee as i 
-    where o.dept = i.dept and post='assistant'); 
+    where o.dept_id = i.dept_id and post='assistant'); 
 ```
 
 ## 选项
@@ -37,17 +37,17 @@ where not exists(
 ### A
 
 ```sql
-select id, name, dept
+select id, name, dept_id
 from employee as o
 where exists(
     select * 
     from employee as i 
-    where o.dept = i.dept and post='assistant'); 
+    where o.dept_id = i.dept_id and post='assistant'); 
 ```
 
 ### B
 ```sql
-select id, name, dept 
+select id, name, dept_id 
 from employee as o
 where 'assistant' != exists(
     select post 
@@ -57,10 +57,10 @@ where 'assistant' != exists(
 ### C
 
 ```sql
-select id, name, dept 
+select id, name, dept_id 
 from employee as o
 where 'assistant' = not exists(
     select post 
     from employee as i 
-    where o.dept = i.dept); 
+    where o.dept_id = i.dept_id); 
 ```
\ No newline at end of file