–1.使用等值連線，顯示員工的編號，姓名，部門名，使用表別名簡化
select e.employee_id,e.first_name,d.department_name
from employees e,departments d
where e.department_id=d.department_id ;c

–2.使用非等值連線，顯示員工的編號，姓名，月薪，工資級別
select e.employee_id , e.first_name , salary , m.e_groun
from employees e , money m
where e.salary between m.hire_money and m.end_money;

–3.使用外連線，按部門10,20,30,40號，統計各部門員工人數，顯示部門號，部門名，人數
select d.department_id ,d.department_name,count(e.employee_id)
from departments d ,employees e
where d.department_id(+)=e.department_id and d.department_id in (10,20,30,40)
group by d.department_id,d.department_name;

–4.使用自連線，顯示”SMITH的老闆是FORD”這種格式，表示層次關聯的資料，用自連線
select e1.first_name ||’的老闆是’||e2.first_name as word
from employees e1,employees e2
where e1.manager_id=e2.employee_id;

–5.查詢部門名為’SALES’的員工資訊
select *
from employees e,departments d
where e.department_id=d.department_id and d.department_name=’Sales’;

–6.查詢每個部門的最低工資
select e.department_id, min(e.salary),d.department_name
from employees e ,departments d
where e.department_id(+)=d.department_id
group by e.department_id,d.department_name;

select department_id , min(salary)
from employees
group by department_i;

–7.查詢工資比20號部門[任意any] 一個員工[低<] 的員工資訊(多行子查詢，any關鍵字)
select *
from employees
where salary< any(select salary
from employees
where department_id=20);

–8.查詢出平均工資小於5000的部門資訊
select e.department_id,d.department_name,avg(salary)
from departments d,employees e
where d.department_id(+)=e.department_id
group by e.department_id,d.department_name
having avg(salary)<5000;