DEPTNO DNAME COUNT(*)
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10 ACCOUNTING 3
20 RESEARCH 5
30 SALES 6
13．查询各个部门员工工资大于平均工资（平均工资包括所有员工）的人数和员工职位(子查询)
SQL> select count(*),job from emp where sal>(select avg(sal) from emp) group by job;
14．查询工资相同的员工的工资和姓名（子查询）
SQL> select sal,ename from emp e where(select count(*) from emp where sal=e.sal group by sal)>1;
或
SQL> select e.sal,e.ename from emp e,emp e1 where e.sal=e1.sal and e.ename<>e1.ename;