上一篇SQL语句的答案(①-⑧)

自己写的。不过在PL/SQL中运行过的，应该米问题
①select * from employees;
select employees.employee_id 员工编号, employees.first_name||'_'||employees.last_name 员工姓名 from employees;
②select distinct employees.department_id from employees where employees.department_id is not null;
③select * from employees order by employees.first_name;
select * from employees order by employees.first_name, employees.last_name desc;
④select employees.salary*2 新工资 from employees;
select employees.salary-100 减工资 from employees;
select employees.hire_date+10 新日期from employees;
⑤同①
⑥select * from employees where employees.salary>=10000;
select * from employees where employees.department_id!=80;
select * from employees where employees.first_name in ('David','Guy');
select * from employees where employees.phone_number like '650%';
select * from employees where employees.employee_id between 100 and 200;
⑦select * from employees where employees.job_id='ST_MAN' and employees.salary>2000;
select * from employees where employees.manager_id='100' or employees.department_id='80';
select * from employees where not employees.phone_number like '650%';
⑧select * from employees where employees.department_id is null;
select * from employees where employees.department_id is not null;
select employees.employee_id, nvl(employees.department_id,'0') 部门编号 from employees;
select * from employees where employees.employee_id=&a;