SQL数据库几个题目,跪求大神解答啊!

1.select eno,ename,age from emp where job_title="高" and gender=1
2.
3.
4.
5.select emp.dno,dname count(dno) as 部门人数 from emp,dept where emp.dno=dept.dno group by 1 order by 1
6.select emp,dno,,dname,average(salary) 平均工资 from emp,dept where emp.dno=dept.dno group by 1,2 order by 1 having 平均工资>3000

1、 select eno， ename，age from emp where job_title=‘高级’ and gender=1

2、
∏eno， ename，age (φjob_title=‘高级’ and gender=1 (emp))
注:其中的∏表示投影,φ表示选择.

3、

4、create index 索引名 on emp (eno)

5、select dept.dname ，count（emp .eno） from dept ，emp
where emp.dno=dept.dno
group by dename

6、select dept.dno ,dept.dname, avg(salary) from dept ，emp
where emp.dno=dept.dno and salary>3000
group by dename ,dno