2020-12-15学习MySQL笔记

最近比较忙，今天继续有空
题目来源https://blog.youkuaiyun.com/mrbcy/article/details/68965271
今天的题目：查询“张旭“教师任课的学生成绩
我的做法：

SELECT
	students.sno as sno,
	sname,
	cname,
	degree 
FROM
	students,
	scores,
	courses,
	teachers 
WHERE
	students.sno = scores.sno 
	AND scores.cno = courses.cno 
	AND courses.tno = teachers.tno 
	AND teachers.tname = '张旭';

形成结果;

students.sno as sno
为什么这里会这么写
因为如果单独写sno，会报错：
1052 - Column ‘sno’ in field list is ambiguous
造成sno取值指向不明，所以要特指哪个表里的sno