mysql模糊查询is null

①=或<>不能用于判断null值

②is null或is not null 可以判断null值

案例1：查询没有奖金的员工名和奖金率

SELECT
	last_name,
	commission_pct
FROM
	employees
WHERE
	commission_pct IS NULL;

案例2：查询有奖金的员工名和奖金率

SELECT
	last_name,
	commission_pct
FROM
	employees
WHERE
	commission_pct IS NOT NULL;

错误的写法：

SELECT
	last_name,
	commission_pct
FROM
	employees

WHERE 
	salary IS 12000;