以下各个题目将用到上图的4个表，其关联关系如图所示。这个四个表中字段的具体情况参看如下内容：
EMPLOYEES(employee_id number(6) not null,first_name varchar2(20),last_name varchar2(25) not null,email varchar2(25) not null,phone_number varchar2(20),hire_date date not null,job_id varchar2(10) not null,salary number(8,2),commission_pct number(2,2),manager_id number(6),department_id number(4))
DEPT(department_id number(4) not null,department_name varchar2(30) not null,manager_id number(6),location_id number(4))
locations(location_id number(4) not null,city varchar2(20))
job_grades(grade_level varchar2(3),lowest_sal number,highest_sal number)
1. 写一个查询显示当前日期，列标签显示为 Date。
SELECT sysdate "Date" FROM dual;
2. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。对每一个雇员，显示employee number、last_name、salary和 salary 增加 15%，并且表示成整数，列标签显示为 New Salary
SELECT employee_id, last_name, salary, ROUND(salary * 1.15, 0) "New Salary" FROM employees;
3. 在2题的基础上，添加一个列，该列从新薪水 New Salary 列（新薪水指的是增加15%以后的薪水）中减去旧薪水，列标签为Increase。
SELECT employee_id, last_name, salary, ROUND(salary * 1.15, 0) "New Salary", ROUND(salary * 1.15, 0) - salary "Increase" FROM employees;
4. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。写一个查询用首字母大写，其它字母小写显示雇员的last names，显示名字的长度，对所有名字开始字母是 J、A或 M 的雇员，给每列一个适当的标签。用雇员的last names 排序结果。
SELECT INITCAP(last_name) "Name", LENGTH(last_name) "Length" FROM employees WHERE last_name LIKE 'J%' OR last_name LIKE 'M%' OR last_name LIKE 'A%' ORDER BY last_name;
5. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。对每一个雇员，显示其的last name，并且计算从雇员受雇日期到今天的月数，列标签MONTHS_WORKED。按受雇月数排序结果，四舍五入月数到最靠近的整数月。
SELECT last_name, ROUND(MONTHS_BETWEEN (SYSDATE, hire_date)) MONTHS_WORKED FROM employees ORDER BY MONTHS_BETWEEN(SYSDATE, hire_date);
6. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。写一个查询对每个雇员做计算：<雇员的 last name> earns <salary> monthly but wants <3倍 salary>。列标签 Dream Salaries。
SELECT last_name || ' earns ' || TO_CHAR(salary, 'fm$99,999.00') || ' monthly but wants ' || TO_CHAR(salary * 3, 'fm$99,999.00') || '.' "Dream Salaries" FROM employees;
7. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。创建一个查询显示所有雇员的last name 和 salary。格式化为15 个字符长度，用 $ 左填充，列标签 SALARY。
SELECT last_name, LPAD(salary, 15, '$') SALARY FROM employees;
8. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。显示每一个雇员的last name、hire date 和 salary 检查日期，该日期是服务六个月后的第一个星期一，列标签 REVIEW。格式化日期显示看起来象“Monday, the Thirty-First of July, 2000” 的样子。
SELECT last_name, hire_date, TO_CHAR(NEXT_DAY(ADD_MONTHS(hire_date, 6),'MONDAY'), 'fmDay, "the" Ddspth "of" Month, YYYY') REVIEW FROM employees;
9. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。显示last name、hire date 和 雇员开始工作的周日，列标签 DAY，用星期一作为周的起始日排序结果。
SELECT last_name, hire_date, TO_CHAR(hire_date, 'DAY') DAY
FROM employees ORDER BY TO_CHAR(hire_date - 1, 'd');
10. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。创建一个查询显示雇员的last names 和 commission (佣金)比率。如果雇员没有佣金，显示 “No Commission”，列标签COMM。
SELECT last_name, NVL(TO_CHAR(commission_pct), 'No Commission') COMM FROM employees;
11. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。创建一个查询显示雇员的last names 并带星号显示他们的年薪，每个星号表示1000美圆。按薪水降序排序数据。列标签为EMPLOYEES_AND_THEIR_SALARIES。
SELECT rpad(last_name, 8)||' '|| rpad(' ', (salary*12)/1000+1, '*') EMPLOYEES_AND_THEIR_SALARIES FROM employees ORDER BY salary DESC;
12. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。用DECODE 函数，写一个查询，按照下面的数据显示所有雇员的基于 JOB_ID列值的级别。
工作 级别
AD_PRES A
ST_MAN B
IT_PROG C
SA_REP D
ST_CLERK E
不在上面的 0
SELECT job_id, decode (job_id, 'ST_CLERK', 'E', 'SA_REP', 'D', 'IT_PROG', 'C', 'ST_MAN', 'B', 'AD_PRES', 'A', '0') GRADE FROM employees;
13. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。DEPT(department_id,department_name,manager_id,location_id)。写一个查询显示所有雇员的 last name、department number、and department name。
SELECT e.last_name, e.department_id, d.department_name FROM employees e, departments d WHERE e.department_id = d.department_id;
14. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。DEPT(department_id,department_name,manager_id,location_id)。创建一个在部门80 中的所有工作岗位的唯一列表，在输出中包括部门的地点。
SELECT DISTINCT job_id, location_id FROM employees, departments WHERE employees.department_id = departments.department_id AND employees.department_id = 80;
15. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。DEPT(department_id,department_name,manager_id,location_id)。locations(location_id,city)。写一个查询显示所有有佣金的雇员的last name、department name、location ID和城市。
SELECT e.last_name, d.department_name, d.location_id, l.c ity FROM employees e, departments d, locations l WHERE e.department_id = d.department_id AND d.location_id = l.location_id AND e.commission_pct IS NOT NULL;
16. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。DEPT(department_id,department_name,manager_id,location_id)。显示所有在其last names 中有一个小写 a 的雇员的last name 和 department name。
SELECT last_name, department_name FROM employees, departments WHERE employees.department_id = departments.department_id AND last_name LIKE '%a%';
17. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。DEPT(department_id,department_name,manager_id,location_id)。locations(location_id,city)。写一个查询显示那些工作在Toronto 的所有雇员的 last name、job、department number和 department name。
SELECT e.last_name, e.job_id, e.department_id, d.department_name FROM employees e JOIN departments d ON (e.department_id = d.department_id) JOIN locations l ON (d.location_id = l.location_id) WHERE LOWER(l.city) = 'toronto';
18. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。显示雇员的last name 和 employee number 连同他们的经理的 last name 和 manager number。列标签分别为Employee、Emp#、Manager和 Mgr#
SELECT w.last_name "Employee", w.employee_id "EMP#", m.last_name "Manager", m.employee_id "Mgr#" FROM employees w join employees m ON (w.manager_id = m.employee_id);
19. 在18题基础上，显示所有雇员包括 King，他没有经理。用雇员号排序结果
SELECT w.last_name "Employee", w.employee_id "EMP#", m.last_name "Manager", m.employee_id "Mgr#" FROM employees w LEFT OUTER JOIN employees m ON (w.manager_id = m.employee_id);
20. EMPLOYEES(employee_id,first_name,last_name,email,phone_number,hire_date,job_id,salary,commission_pct,manager_id,department_id)。创建一个查询显示所有与被指定雇员工作在同一部门的雇员(同事) 的 last names、department numbers。给每列一个适当的标签。
SELECT e.department_id department, e.last_name employee, c.last_name colleague FROM employees e JOIN employees c ON (e.department_id = c.department_id) WHERE e.employee_id <> c.employee_id ORDER BY e.department_id, e.last_name, c.last_name;