sql语句练习：
https://blog.csdn.net/mrbcy/article/details/68965271
https://blog.csdn.net/flycat296/article/details/63681089
hive语句综合练习
以下网址中的表为背景表，完成以下练习题：
https://blog.csdn.net/mrbcy/article/details/68965271
1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
SELECT a.* ,b.s_score AS 01_score,c.s_score AS 02_score FROM
student a
LEFT JOIN score b ON a.s_id=b.s_id AND b.c_id='01'
LEFT JOIN score c ON a.s_id=c.s_id AND c.c_id = '02' WHERE b.s_score>c.s_score;
2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
SELECT a.* ,b.s_score AS 01_score,c.s_score AS 02_score FROM
student a LEFT JOIN score b ON a.s_id=b.s_id AND b.c_id='01'
JOIN score c ON a.s_id=c.s_id AND c.c_id='02' WHERE b.s_score<c.s_score;
3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩
SELECT b.s_id,b.s_name,ROUND(AVG(a.s_score),2) AS avg_score FROM
student b
JOIN score a ON b.s_id = a.s_id
GROUP BY b.s_id,b.s_name HAVING ROUND(AVG(a.s_score),2)>=60;
4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩
-- (包括有成绩的和无成绩的)
SELECT b.s_id,b.s_name,ROUND(AVG(a.s_score),2) AS avg_score FROM
student b
LEFT JOIN score a ON b.s_id = a.s_id
GROUP BY b.s_id,b.s_name HAVING ROUND(AVG(a.s_score),2)<60
UNION ALL
SELECT a.s_id,a.s_name,0 AS avg_score FROM
student a
WHERE a.s_id NOT IN (
SELECT DISTINCT s_id FROM score);
-- 5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩
SELECT a.s_id,a.s_name,COUNT(b.c_id) AS sum_course,SUM(b.s_score) AS sum_score FROM
student a
LEFT JOIN score b ON a.s_id=b.s_id
GROUP BY a.s_id,a.s_name;
-- 6、查询"李"姓老师的数量
select count(t_id) from techer where t_name like '李%';
-- 7、查询学过"张三"老师授课的同学的信息
SELECT a.*
FROM student a LEFT JOIN score b ON a.s_id = b.s_id WHERE b.c_id IN (
SELECT c.c_id
FROM course c LEFT JOIN techer t ON c.t_id = t.t_id WHERE t.t_name = '张三'
) ;
-- 8、查询没学过"张三"老师授课的同学的信息
SELECT s.*
FROM student s LEFT JOIN (
SELECT a.s_id
FROM student a LEFT JOIN score b ON a.s_id = b.s_id WHERE b.c_id IN (
SELECT c.c_id
FROM course c LEFT JOIN techer t ON c.t_id = t.t_id WHERE t.t_name = '张三'
)
) ss ON s.s_id = ss.s_id WHERE ss.s_id IS NULL;
-- 9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息
select a.* from
student a,score b,score c
where a.s_id = b.s_id and a.s_id = c.s_id and b.c_id='01' and c.c_id='02';
-- 10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
SELECT qq.*
FROM (
SELECT s.*
FROM student s LEFT JOIN score sco ON s.s_id = sco.s_id LEFT JOIN course c ON sco.c_id = c.c_id WHERE c.c_id='01'
LEFT JOIN (
SELECT stu.*
FROM student stu LEFT JOIN score mysco ON stu.s_id = mysco.s_id LEFT JOIN course cou ON mysco.c_id = cou.c_id WHERE cou.c_id='02'
) pp
ON qq.s_id = pp.s_id WHERE pp.s_id IS NULL;
-- 11、查询没有学全所有课程的同学的信息
SELECT ss.s_id
FROM (
SELECT stu.s_id,COUNT(stu.s_id) AS num
FROM student stu LEFT JOIN score sco ON stu.s_id = sco.s_id LEFT JOIN course cou ON sco.c_id = cou.c_id
GROUP BY stu.s_id
) ss WHERE ss.num < 3
-- 12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息
SELECT stu.*
FROM student stu LEFT JOIN
(
SELECT s.s_id
FROM score s WHERE s.c_id IN(
SELECT c_id FROM score WHERE s_id = '01'
)GROUP BY s_id
) pp ON stu.s_id = pp.s_id WHERE pp.s_id IS NOT NULL;