一、查询没有奖金，且工资小于18000的salary，last_name
SELECT
last_name,
salary
FROM
employees
WHERE
commission_pct IS NULL AND salary<18000;
二、查询employees表中，job_id不为‘IT’或者工资为120000的员工信息
SELECT
*
FROM
employees
WHERE
job_id<>'IT' or salary=12000;
三、查看部门departments表的结构，查询效果如下
DESC departments;
四、查询部门departments表中涉及到了哪些位置编号
SELECT DISTINCT location_id
FROM departments
五、面试题
试问：select *from employees；和select * from employees where commission_pct like '%%' and last_name '%%'结果是否一样？并说明原因。
不一样！
如果判断的字段有null值，两个结果不一样。
