fixed structure bugs

data/2.PostgreSQL中阶/2.服务端编程/1.聚合和分组/salary.md

@@ -47,7 +47,6 @@ select id, name, dept, max(salary) from employee group by dept, id, name having
 
 ### 结构错误
 
-### group by 不对
 
 ```postgresql
 select id, name, dept, max(salary) from employee where salary=max(salary) group by dept;