--4.选择雇用时间在1998-02-01到1998-05-01之间的员工姓名，job_id和雇用时间
select last_name,job_id,hire_date
from employees
where to_char(hire_date,‘yyyy-mm-dd‘) between ‘1998-02-01‘ and ‘1998-05-01‘
--5.选择在20或50号部门工作的员工姓名和部门号
select last_name,department_id
from employees
--where department_id between 20 and 50
where department_id >=20 and department_id <=50
--6.选择在1994年雇用的员工的姓名和雇用时间
select last_name,hire_date
from employees
--where to_char(hire_date,‘yyyy‘)=‘1994‘
where hire_date like ‘%94‘
--7.选择公司中没有管理者的员工姓名及job_id
select last_name,job_id
from employees
where manager_id is null
--8.选择公司中有奖金的员工姓名，工资和奖金级别
select last_name,salary,commission_pct
from employees
where commission_pct is not null
--9.选择员工姓名的第三个字母是a的员工姓名
select last_name
from employees
where last_name = ‘__a%‘
--10.选择姓名中有字母a和e的员工姓名
select last_name
from employees
where last_name like ‘%a%e%‘ or last_name like ‘%e%a%‘
1.显示系统时间(注：日期+时间)
select to_char(sysdate,‘yyyy-mm-dd hh:mi:ss‘)
from dual
--2.查询员工号，姓名，工资，以及工资提高百分之20%后的结果（new salary）
select department_id,last_name,salary,salary*(1+0.2) "new salary"
from employee01
--将员工的姓名按首字母排序，并写出姓名的长度（length)
select last_name,length(last_name)
from employee01
order by last_name asc
--4.查询各员工的姓名，并显示出各员工在公司工作的月份数（worked_month）。
select last_name,hire_date,round(months_between(sysdate,hire_date),1) worked_month
from employees
--5.查询员工的姓名，以及在公司工作的月份数（worked_month），并按月份数降序排列
select last_name,hire_date,round(months_between(sysdate,hire_date),1) worked_month
from employees
order by worked_month desc
--6.做一个查询，产生下面的结果
--<last_name> earns <salary> monthly but wants <salary*3>
Dream Salary
-------------------------------------------------------------------
King earns $24240 monthly but wants $72720
select last_name || ‘ earns ‘ || to_char(salary,‘$999999‘) || ‘ monthly but wants ‘ || to_char(salary*3,‘$999999‘) "Dream Salary"
from employees
select last_name "Last_name",job_id "Job_id",decode(
job_id,‘AD_PRES‘,‘A‘,
‘ST_MAN‘,‘B‘,
‘IT_PROG‘,‘C‘,
‘SA_REP‘,‘D‘,
‘ST_CLERK‘,‘E‘) "Grade"
from employees