尚硅谷mysql学习笔记

查询

去重

SELECT DISTINCT department_id  FROM employees;

空值参数运算

如果值为null则使用0替换，任何值与null计算都为null

SELECT employee_id,salary "月工资",salary * (1 + IFNULL(commission_pct,0)) * 12 "年工资",commission_pct 
FROM `employees`;