7. 创建一个查询，显示所有员工的姓氏和薪金，将薪金的格式为15个字符，左边加$。将
该列标记为SALARY SELECT last_name,
LPAD(salary, 15, '$') SALARY FROM employees;
8. 显示所有员工的最高薪金、最低薪金、总计薪金和平均薪金。分别将这些列标记为
Maxinmum、Minimum、Sum和Average。将结果舍入到最接近的整数 SQL：
SELECT ROUND(MAX(salary),0) \ROUND(MIN(salary),0) \ROUND(SUM(salary),0) \ROUND(AVG(salary),0) \FROM employees;
9. 显示经理编号以及该经理所管员工的最低薪金。不包括其经理不知是谁的任何员工。不
包括最低薪金未超过$6000的组 SELECT manager_id, MIN(salary) FROM employees
WHERE manager_id IS NOT NULL GROUP BY manager_id
HAVING MIN(salary) > 6000 ORDER BY MIN(salary) DESC;
10. 编写一个查询，以显示赚取佣金的所有的员工的姓氏、部门名称、地点标识以及城市 SELECT e.last_name, d.department_name, d.location_id, l.city 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; 11. 创建一个查询，以显示员工的姓氏、部门编号以及该员工在同一部门的工作的所有员工。
为每一列给出合适的标签
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; 12. 显示King的每个下属员工的姓氏和薪金 SELECT last_name, salary FROM employees
WHERE manager_id = (SELECT employee_id FROM employees
WHERE last_name = 'King' and first_name='Steven');