练习题--MySQL

#一、查询没有奖金，且工资小于18000的salary，last_name
SELECT salary,last_name  FROM  employees
WHERE  salary<18000 AND salary IS NULL;
#查询employees表中，job_id不为 ‘IT’或者工资为12000的员工信息
SELECT * FROM  employees 
WHERE  job_id <> 'IT' OR  salary <=>12000;
#查看部门表的结果
DESC  departments;
#查询部门departments表中涉及到了哪些位置编号
SELECT  location_id FROM  departments;
#经典面试题
#试问：select * from employees;和select * from employees
#where commission_pct like '%%' and last_name like '%%';
SELECT * FROM employees;
SELECT * FROM 
employees 
WHERE commission_pct LIKE '%%' AND last_name LIKE '%%';
#结果不一样，
#如果判断的字段没有null值，那就一样