切换到 oracle的 hr用户下面练习
1. 查询工资大于12000的员工姓名和工资
Select initcap(concat(last_name,first_name)) "姓名",salary from employees where salary>12000;
2. 查询员工号为176的员工的姓名和部门号
select initcap(concat(last_name,first_name)) "姓名",department_id from employees where employee_id = 176;
3. 选择工资不在5000到12000的员工的姓名和工资
select initcap(concat(last_name,first_name)) "姓名", salary from employees where salary<5000 or salary>12000;
4. 选择雇用时间在1908-02-01到1908-05-01之间的员工姓名，job_id和雇用时间
写法一：
select initcap(concat(last_name,first_name)) "姓名",job_id,hire_date from employees where hire_date between '01-2月 -08' and '01-5月 -08';
写法二：
select initcap(concat(last_name,first_name)) "姓名",job_id,hire_date from employees where hire_date between to_date('1908-02-01','YYYY-MM-DD') and to_date('1908-05-01','YYYY-MM-DD');
5. 选择在20或50号部门工作的员工姓名和部门号
写法一：
Select initcap(concat(last_name,first_name)) "姓名",department_id from employees where department_id=20 or department_id=50;
写法二：
select initcap(concat(last_name,first_name)) "姓名",department_id from employees where department_id in (20,50);
6. 选择在1908年雇用的员工的姓名和雇用时间
写法一：
select initcap(concat(last_name,first_name))"姓名",hire_date from employees where hire_date like '%08';
写法二：
select initcap(concat(last_name,first_name))"姓名",hire_date from employees where hire_date between to_date('1908-1-1','YYYY-MM-DD') and to_date('1908-12-31','YYYY-MM-DD');
7. 选择公司中没有管理者的员工姓名及job_id
写法一：
Select initcap(concat(last_name,first_name)) "姓名",job_id from employees where manager_id is null;
写法二：
select initcap(concat(last_name,first_name)) "姓名",job_id from employees where nvl(manager_id,0)=0;
8. 选择公司中有奖金的员工姓名，工资和奖金级别
写法一：
Select initcap(concat(last_name,first_name)) "姓名",salary,commission_pct from employees where commission_pct is not null;
写法二：
Select initcap(concat(last_name,first_name)) "姓名",salary,commission_pct from employees where nvl2(commission_pct, commission_pct,0)>0;
写法三：
select initcap(concat(last_name,first_name)) "姓名", commission_pct from employees where nvl（commission_pct,0)<>0;
9. 选择员工姓名的第三个字母是a的员工姓名
select initcap(concat(last_name,first_name)) "姓名" from employees where initcap(concat(last_name,first_name)) like '__a%';
10. 选择姓名中有字母a和e的员工姓名
select initcap(concat(last_name,first_name)) "姓名" from employees where initcap(concat(last_name,first_name)) like '%a%' and initcap(concat(last_name,first_name)) like '%e%';
11. 显示系统时间
写法一：
Select sysdate from dual;
写法二：
Select current_timestamp from dual;
12. 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 employee_id,initcap(concat(last_name,first_name)) "姓名",salary*1.2 as"new salary" from employees;
13. 将员工的姓名按首字母排序，并写出姓名的长度（length）
Select initcap(concat(last_name,first_name)) "姓名",length(initcap(concat(last_name,first_name))) as"名字长度" from employees order by substr(initcap(concat(last_name,first_name)),1,1);
14. 查询各员工的姓名，并显示出各员工在公司工作的月份数
Select initcap(concat(last_name,first_name)) "姓名",trunc(months_between(sysdate,hire_date),0) "在职时间" from employees;
15. 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 initcap(concat(last_name,first_name)) "姓名",trunc(months_between(sysdate,hire_date),0) "在职时间" from employees order by trunc(months_between(sysdate,hire_date),0) desc;
16.做一个查询，产生下面的结果
<last_name> earns <salary><salary*3>
Dream Salary
King earns $24000 monthly but wants $72000
Select last_name||' earns '||to_char(salary,'$99999')||' monthly but wants '||to_char(salary*3,'$99999') as "Dream Salary" from employees;
17.使用decode函数，按照下面的条件：
job grade
AD_PRES A
ST_MAN B
IT_PROG C
SA_REP D
ST_CLERK E
Others F
产生下面的结果
| Last_name | Job_id | Grade |
| king | AD_PRES | A |
写法一：
写法二：
Select last_name,job_id,
case job_id
when 'AD_PRES' then 'A'
when 'ST_MAN' then 'B'
when 'IT_PROG' then 'C'
when 'SA_REP' then 'D'
when 'ST_CLERK' then 'E'
else 'F' end "Grage" from employees;
18.查询公司员工工资的最大值，最小值，平均值，总和
select max(salary) "最大值",min(salary) "最小值",avg(salary) "平均值",sum(salary) "总和" from employees;
19.查询各job_id的员工工资的最大值，最小值，平均值，总和
select job_id,max(salary) "最大值",min(salary) "最小值",avg(salary) "平均值",sum(salary) "总和" from employees group by job_id;
20.选择具有各个job_id的员工人数
Select job_id,count(*) from employees group by job_id;
21.查询员工最高工资和最低工资的差距（DIFFERENCE）
Select max(salary)-min(salary) as "DIFFERENCE" from employees;
22.查询各个管理者手下员工的最低工资，其中最低工资不能低于6000，没有管理者的员工不计算在内
Select manager_id,min(salary) from employees group by manager_id having min(salary)>=6000 and manager_id is not null;
23.查询所有部门的名字，location_id，员工数量和工资平均值
Select department_name,location_id,count(e.job_id) as "部门总人数",avg(e.salary) as "平均工资" from departments d,employees e where d.department_id=e.department_id group by department_name,location_id;