行子查询和列子查询

-- 16、查询和01号同学所学课程完全一样的学生信息
select group_concat(c_id) from sc group by s_id having s_id = '01'; #找出01所选修的课程


select stu.s_id,group_concat(c_id order by c_id) 选修课程
from stu left join sc on sc.s_id= stu.s_id
group by stu.s_id
having 选修课程 = (select group_concat(c_id order by c_id) from sc group by s_id having s_id = '01');



-- 17、查询至少有一门课与01号同学所学课程一样的学生信息
select c_id
from sc
where s_id='01';

select distinct stu.*
from stu left join sc on sc.s_id= stu.s_id
where c_id in  (select c_id
from sc
where s_id='01');

　　完全匹配，例如第一题中，此时需要将零散的课程号变成一行，用group_concat()函数，行子查询

　　第二题中至少，此时用列子查询不用将其变为一行，，在列中进行in的匹配