SELECT数据查询例题1

#一、查询没有奖金，且工资小于18000 salary,last_name 并排序。

SELECT salary,last_name
FROM employees
WHERE commission_pct IS NULL
AND salary<18000
ORDER BY salary DESC;

#二、查询employess表中，job_id不为‘IT’，或者工资为12000的员工信息
#WHERE job_id <>IT

SELECT *
FROM employees
WHERE job_id NOT IN ('IT')
OR salary=12000;

/*三、经典面试题
试问：SELECT * FROM empoyees; 和
SELRCT * FROM empoyees
WHERE commission_pct
LIKE ‘%%’
AND last_name LIKE ’%%‘;
结果是否一样？并说明理由。

不一样

如果判断的字段有null值

and 换成 or就行了

*/