mysql is 、is not 和 <=>

SELECT 
    last_name,
    commission_pct
FROM
    employees
WHERE
    commission_pct IS NULL;

#案例：查询有奖金

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

安全等于: <=>,也可以判断null值和普通类型的值

SELECT 
    last_name,
    commission_pct
FROM 
    employees
WHERE
    commission_pct <=> NULL;

mysql is 、is not 和 <=>

原文：https://blog.51cto.com/14437184/2435252