--1.查找到同时存在" 01 "课程和" 02 "课程的情况

-- 创建表及数据信息,在第一篇随笔中.

-- 1.通过两张子表得到课程01和课程02的成绩信息，

 

-- 2.笛卡儿积合并两张表，最后WHERE筛选

SELECT * 
FROM (SELECT * FROM sc WHERE Cid = 01) AS a,(SELECT * FROM sc WHERE Cid = 02) AS b 
WHERE a.Sid = b.SId;

 -- 3.去除冗余;

SELECT a.Sid,a.score 01_score,b.score 02_score
FROM (SELECT * FROM sc WHERE Cid = 01) AS a,(SELECT * FROM sc WHERE Cid = 02) AS b 
WHERE a.Sid = b.Sid ;