USE testdb;

DROP TABLE Student;
DROP TABLE Course;
DROP TABLE SC;
DROP TABLE Teacher;





-- 語法：
SELECT select_list　　　 
FROM table_name　　 
[ WHERE search_condition ]　　 
[ GROUP BY group_by_expression ]　　 
[ HAVING search_condition ]　　 
[ ORDER BY order_expression [ ASC | DESC ] ] 
[LIMIT m,n] 
  
-- 示例：
-- limit 0,10是從第一條開始,取10條資料
SELECT classNo  FROM table_name  
GROUP BY classNo   
HAVING(AVG(成績)>70) 
ORDER BY classNo  
LIMIT 0,10

IFNULL



-- Student(S#,Sname,Sage,Ssex) 學生表
CREATE TABLE Student(
	sid INT PRIMARY KEY,
	sname VARCHAR(20) NOT NULL DEFAULT '',
	sage INT,
	ssex VARCHAR(2)
)

-- Course(C#,Cname,T#) 課程表 
CREATE TABLE Course(
	cid INT PRIMARY KEY,
	cname VARCHAR(20) NOT NULL DEFAULT '',
	tid INT
)

-- Teacher(T#,Tname) 教師表
CREATE TABLE Teacher(
	tid INT PRIMARY KEY,
	tname VARCHAR(20) NOT NULL DEFAULT ''
)

-- SC(S#,C#,score) 成績表 
CREATE TABLE SC(
	sid INT ,
	cid INT ,
	score INT
)



-- 學生表測試資料
INSERT INTO Student VALUES(01 , '趙雷' , 18 , '男');
INSERT INTO Student VALUES(02 , '錢電' , 19 , '男');
INSERT INTO Student VALUES(03 , '孫風' , 22 , '男');
INSERT INTO Student VALUES(04 , '李雲' , 19 , '男');
INSERT INTO Student VALUES(05 , '周梅' , 20 , '女');
INSERT INTO Student VALUES(06 , '吳蘭' , 19 , '女');
INSERT INTO Student VALUES(07 , '鄭竹' , 21 , '女');
INSERT INTO Student VALUES(08 , '王菊' , 18 , '女');

-- 課程表測試資料
INSERT INTO Course VALUES(01 , '語文' , 02);
INSERT INTO Course VALUES(02 , '數學' , 01);
INSERT INTO Course VALUES(03 , '英語' , 03);
 
-- 教師表測試資料
INSERT INTO Teacher VALUES(01 , '張三');
INSERT INTO Teacher VALUES(02 , '李四');
INSERT INTO Teacher VALUES(03 , '王五');
INSERT INTO Teacher VALUES(04 , '李六');

COMMIT;
 
-- 成績表測試資料
INSERT INTO SC VALUES(01 , 01 , 80);
INSERT INTO SC VALUES(01 , 02 , 90);
INSERT INTO SC VALUES(01 , 03 , 99);
INSERT INTO SC VALUES(02 , 01 , 70);
INSERT INTO SC VALUES(02 , 02 , 60);
INSERT INTO SC VALUES(02 , 03 , 80);
INSERT INTO SC VALUES(03 , 01 , 80);
INSERT INTO SC VALUES(03 , 02 , 80);
INSERT INTO SC VALUES(03 , 03 , 80);
INSERT INTO SC VALUES(04 , 01 , 50);
INSERT INTO SC VALUES(04 , 02 , 30);
INSERT INTO SC VALUES(04 , 03 , 20);
INSERT INTO SC VALUES(05 , 01 , 76);
INSERT INTO SC VALUES(05 , 02 , 87);
INSERT INTO SC VALUES(06 , 01 , 31);
INSERT INTO SC VALUES(06 , 03 , 34);
INSERT INTO SC VALUES(07 , 02 , 89);
INSERT INTO SC VALUES(07 , 03 , 98);
INSERT INTO SC VALUES(08 , 01 , 31);
INSERT INTO SC VALUES(08 , 03 , 34);
INSERT INTO SC VALUES(08 , 02 , 89);


-- Student(S#,Sname,Sage,Ssex) 學生表 
-- Course(C#,Cname,T#) 課程表 
-- SC(S#,C#,score) 成績表 
-- Teacher(T#,Tname) 教師表

-- 1、查詢“01”課程比“02”課程成績高的所有學生的學號；
SELECT a.sid FROM (SELECT sid, score FROM sc WHERE cid=01) a,(SELECT sid ,score FROM sc WHERE cid=02) b WHERE a.score > b.score AND a.sid= b.sid;

SELECT a.sid FROM student a LEFT JOIN SC b ON b.cid=01 AND a.sid=b.sid LEFT JOIN SC c ON c.cid=02 AND a.sid=c.sid WHERE b.score>c.score;

-- 2、查詢平均成績大於60分的同學的學號和平均成績；
SELECT sid, AVG(score) FROM sc GROUP BY sid HAVING AVG(score)>60;

-- 3、查詢所有同學的學號、姓名、選課數、總成績；
SELECT s.sid, sname, COUNT(cid), AVG(score) FROM student s LEFT JOIN sc ON s.sid = sc.sid GROUP BY sc.sid;

-- 4、查詢姓“李”的老師的個數；
SELECT COUNT(DISTINCT(tname)) FROM Teacher WHERE tname LIKE '李%';

-- 5、查詢沒學過“王五”老師課的同學的學號、姓名；
SELECT sid, sname FROM student WHERE sid NOT IN(SELECT DISTINCT(s.sid) FROM student s, Course c, Teacher t, sc WHERE s.sid = sc.sid AND sc.cid = c.cid AND c.tid = t.tid AND t.tname = '王五'); -- 效率低

SELECT sid, sname FROM student s1 LEFT JOIN (SELECT DISTINCT(s.sid) id FROM student s, Course c, Teacher t, sc WHERE s.sid = sc.sid AND sc.cid = c.cid AND c.tid = t.tid AND t.tname = '王五') AS s2 ON s1.sid = s2.id WHERE s2.id IS NULL; -- 效率相對高

-- 6、查詢學過“01”並且也學過編號“02”課程的同學的學號、姓名；
SELECT DISTINCT(s.sid), sname FROM student s, Course c, SC WHERE s.sid = sc.sid AND c.cid = sc.cid AND c.cid = 01;
SELECT DISTINCT(s.sid), sname FROM student s, Course c, SC WHERE s.sid = sc.sid AND c.cid = sc.cid AND c.cid = 02;

SELECT DISTINCT(s.sid), sname FROM student s, Course c, SC WHERE s.sid = sc.sid AND c.cid = sc.cid AND c.cid = 01 AND s.sid IN (SELECT sid FROM SC WHERE cid = 02);

-- 7、查詢學過“王五”老師所教的所有課的同學的學號、姓名；
SELECT s.sid, sname FROM Student s, Course c, Teacher t, SC WHERE s.sid = sc.sid AND c.cid = sc.cid AND t.tid = c.tid AND t.tname = '王五';

-- 8、查詢課程編號“002”的成績比課程編號“001”課程低的所有同學的學號、姓名；
SELECT s.sid, sname FROM student s, (SELECT sid, score FROM SC WHERE cid = 01) sc1, (SELECT sid, score FROM SC WHERE cid = 02) sc2 WHERE sc1.sid = s.sid AND sc2.sid = s.sid AND sc1.score > sc2.score;

-- 9、查詢所有課程成績小於60分的同學的學號、姓名；
SELECT sid, sname FROM student WHERE sid NOT IN (SELECT sid FROM sc WHERE sc.score > 60);

-- 10、查詢沒有學全所有課的同學的學號、姓名；
SELECT sid, sname FROM student WHERE sid IN(SELECT sid FROM sc GROUP BY sid HAVING COUNT(sid) < (SELECT COUNT(cid) FROM Course)); -- 巢狀，效率相對低
 
SELECT s.sid, s.sname FROM student s, sc WHERE s.sid = sc.sid GROUP BY sc.sid HAVING COUNT(sc.sid) < (SELECT COUNT(cid) FROM Course);

-- 11、查詢至少有一門課與學號為“08”的同學所學相同的同學的學號和姓名；
SELECT DISTINCT(s.sid), s.sname FROM student s, sc WHERE s.sid = sc.sid AND cid IN(SELECT cid FROM sc WHERE sid = 08); -- 巢狀

-- 12、查詢至少學過學號為“01”同學所有一門課的其他同學學號和姓名；
SELECT DISTINCT(s.sid), s.sname FROM student s, sc WHERE s.sid = sc.sid AND s.sid <> 08 AND cid IN(SELECT cid FROM sc WHERE sid = 08);

-- 13、把“SC”表中“王五”老師教的課的成績都更改為此課程的平均成績；--------xxx
UPDATE SC SET score = (
SELECT a.avgs FROM (
SELECT AVG(score) avgs FROM Course c, Teacher t,SC 
WHERE c.cid = sc.cid AND c.tid = t.tid AND t.tname = '王五') a )
WHERE sc.cid =(
SELECT b.cid FROM (
SELECT DISTINCT c.cid 
FROM Course c, Teacher t,SC 
WHERE c.cid = sc.cid AND c.tid = t.tid AND t.tname = '王五') b );



SELECT * FROM sc s
LEFT JOIN course c ON s.cid=c.cid
LEFT JOIN teacher t ON t.tid=c.tid
WHERE t.tname='王五';

SELECT s.sid,AVG(s.score) AVG,t.tname FROM sc s
LEFT JOIN course c ON s.cid=c.cid
LEFT JOIN teacher t ON t.tid=c.tid
WHERE t.tname='王五' GROUP BY c.cid;

UPDATE sc SET score=(
SELECT a.avg FROM (
SELECT AVG(s.score) AVG FROM sc s
LEFT JOIN course c ON s.cid=c.cid
LEFT JOIN teacher t ON t.tid=c.tid
WHERE t.tname='王五' GROUP BY c.cid
) a
)
WHERE sid IN (
SELECT b.sid FROM (
SELECT s.sid FROM sc s
LEFT JOIN course c ON s.cid=c.cid
LEFT JOIN teacher t ON t.tid=c.tid
WHERE t.tname='王五'
)b
);


-- 14、查詢和“02”號的同學學習的課程完全相同的其他同學學號和姓名；    -- 重點記一下
SELECT s.sid, s.sname FROM student s, sc WHERE s.sid = sc.sid AND sc.cid IN (SELECT cid FROM sc WHERE sid = 02) GROUP BY sc.sid HAVING COUNT(sc.sid) = (SELECT COUNT(sid) FROM sc WHERE sid = 02);

-- 15、刪除學習“王五”老師課的SC表記錄；
DELETE FROM sc WHERE cid = (SELECT cid FROM course c, teacher t WHERE c.tid = t.tid AND tname = '王五');

-- 16、向SC表中插入一些記錄，這些記錄要求符合以下條件：沒有上過編號03課程的同學學號、02號課的平均成績；-----回過頭來弄懂！
INSERT INTO sc SET sid = (SELECT DISTINCT(sid) FROM sc WHERE cid <> 03), cid = 03, score = (SELECT AVG(score) FROM sc WHERE sid = 02));

INSERT SC SELECT Sid, 02,(SELECT AVG(score) FROM SC WHERE Cid=02) FROM Student WHERE Sid NOT IN (SELECT Sid FROM SC WHERE Cid=02); 

-- 17、按平均成績從高到低顯示所有學生的“數學”、“英語”、“語文”三門的課程成績，按如下形式顯示：學生ID,數學,英語,語文,有效課程數,有效平均分 ------
SELECT Sid AS 學生ID 
,(SELECT score FROM SC WHERE SC.Sid=t.Sid AND Cid=02) AS 數學 
,(SELECT score FROM SC WHERE SC.Sid=t.Sid AND Cid=03) AS 英語 
,(SELECT score FROM SC WHERE SC.Sid=t.Sid AND Cid=01) AS 語文 
,COUNT(*) AS 有效課程數, AVG(t.score) AS 平均成績 
FROM SC AS t 
GROUP BY Sid
ORDER BY AVG(t.score);

-- 18、查詢各科成績最高和最低的分：以如下形式顯示：課程ID，最高分，最低分
SELECT DISTINCT l.cid AS 課程ID, h.score AS 最高分, l.score AS 最低分 
FROM sc AS h ,sc AS l 
WHERE h.cid = l.cid 
AND h.score =(SELECT MAX(score) FROM sc WHERE cid = l.cid) 
AND l.score = (SELECT MIN(score) FROM sc WHERE cid = l.cid);

-- 19、按各科平均成績從低到高和及格率的百分數從高到低順序查詢 -- 100 * SUM(CASE WHEN ISNULL(score,0)>=60 THEN 1 ELSE 0 END)/COUNT(*) AS 及格百分數
SELECT cid AS 課程號, AVG(score) AS 平均成績, 100 * SUM(CASE WHEN score >=60 THEN 1 ELSE 0 END)/COUNT(*) AS 及格百分數 FROM sc GROUP BY cid ORDER BY (100 * SUM(CASE WHEN score>=60 THEN 1 ELSE 0 END)/COUNT(*)) DESC;

-- 20、查詢如下課程平均成績和及格率的百分數(用"1行"顯示): 語文，英語
SELECT cid AS 課程號, AVG(score) AS 平均成績, 100 * SUM(CASE WHEN score >=60 THEN 1 ELSE 0 END)/COUNT(*) AS 及格百分數 FROM sc WHERE cid = 01 OR cid = 03 GROUP BY cid;

-- 21、查詢不同老師所教不同課程平均分從高到低顯示
SELECT tname 老師姓名, cname 課程名, AVG(score) 平均成績 FROM teacher t, course c, sc WHERE t.tid = c.tid AND c.cid = sc.cid GROUP BY t.tid ORDER BY AVG(score) DESC;

-- 22、查詢如下課程成績第3名到第6名的學生成績單：語文（01）,英語（03） 格式如下：[學生ID], [學生姓名], 語文, 英語, 平均成績
SELECT s.sid, s.sname,IFNULL(cn.score,0) 語文, IFNULL(en.score,0) 英語, (IFNULL(cn.score,0)+IFNULL(en.score,0))/2 平均分 
FROM student s 
LEFT JOIN sc cn ON cn.sid = s.sid AND cn.cid = 01 
LEFT JOIN sc en ON en.sid = s.sid AND en.cid = 03 
ORDER BY 平均分 DESC LIMIT 3,3;

-- 23、統計列印各科成績,各分數段人數:課程ID,課程名稱,[100-85],[85-70],[70-60],[ <60]
SELECT c.cid, c.cname, 
SUM(CASE WHEN score BETWEEN 85 AND 100 THEN 1 ELSE 0 END) AS 優秀,
SUM(CASE WHEN score BETWEEN 75 AND 85 THEN 1 ELSE 0 END) AS 良好,
SUM(CASE WHEN score BETWEEN 60 AND 75 THEN 1 ELSE 0 END) AS 及格,
SUM(CASE WHEN score < 60 THEN 1 ELSE 0 END) AS 不及格
FROM course c, sc 
WHERE c.cid = sc.cid
GROUP BY sc.cid;

SELECT c.cid AS 課程ID, c.cname AS 課程名稱, 
SUM(CASE WHEN score BETWEEN 85 AND 100 THEN 1 ELSE 0 END) AS 優秀, 
SUM(CASE WHEN score BETWEEN 75 AND 85 THEN 1 ELSE 0 END) AS 良好, 
SUM(CASE WHEN score BETWEEN 60 AND 75 THEN 1 ELSE 0 END) AS 及格,
SUM(CASE WHEN score < 60 THEN 1 ELSE 0 END) 不及格 
FROM course c, sc 
WHERE c.cid = sc.cid
GROUP BY c.cid;

-- 24、查詢學生平均成績及其名次
SELECT sid 學號, AVG(score) 平均成績 FROM sc GROUP BY sid ORDER BY AVG(score) DESC;

SELECT 1+(SELECT COUNT( DISTINCT 平均成績)
FROM (SELECT sid,AVG(score) 平均成績
FROM SC
GROUP BY sid
) t1
WHERE 平均成績 > t2.平均成績) 名次,
sid AS 學生學號, 平均成績
FROM (SELECT sid,AVG(score) 平均成績
FROM sc
GROUP BY sid
) t2
ORDER BY 平均成績 DESC;


SELECT 1+(SELECT COUNT( DISTINCT 平均成績) 
FROM (SELECT Sid,AVG(score) AS 平均成績 
FROM SC 
GROUP BY Sid 
) AS T1 
WHERE 平均成績 > T2.平均成績) AS 名次, 
Sid AS 學生學號,平均成績 
FROM (SELECT Sid,AVG(score) 平均成績 
FROM SC 
GROUP BY Sid 
) AS T2 
ORDER BY 平均成績 DESC; 


-- 25、查詢各科成績前三名的記錄:(不考慮成績並列情況) --------------xxxxx
SELECT cid 課程ID, score 成績 FROM sc ORDER BY cid LIMIT 0,3;

SELECT sid 學號, cid 課程ID, score 成績 FROM sc WHERE cid = 1 ORDER BY score DESC LIMIT 0,3;
SELECT sid 學號, cid 課程ID, score 成績 FROM sc WHERE cid = 2 ORDER BY score DESC LIMIT 0,3;
SELECT sid 學號, cid 課程ID, score 成績 FROM sc WHERE cid = 3 ORDER BY score DESC LIMIT 0,3;

-- 26、查詢每門課程被選修的學生數
SELECT cid, COUNT(sid) FROM sc GROUP BY cid;

-- 27、查詢出只選修了兩門課程的全部學生的學號和姓名
SELECT s.sid, s.sname FROM student s, sc WHERE s.sid = sc.sid GROUP BY sc.sid HAVING COUNT(sc.sid) = 2;

-- 28、查詢男生、女生人數
SELECT COUNT(sid) 男生人數 FROM student WHERE ssex = '男';
SELECT COUNT(sid) 女生人數 FROM student WHERE ssex = '女';

-- 29、查詢姓“王”的學生名單
SELECT * FROM student WHERE sname LIKE '王%';

-- 30、查詢同名同性學生名單，並統計同名人數
SELECT sname 姓名, COUNT(*) 人數 FROM student GROUP BY sname,ssex HAVING COUNT(*) >= 2;

-- 31、1981年出生的學生名單(注：Student表中Sage列的型別是DATETIME) 
原題目答案：
SELECT Sname, CONVERT(CHAR (11),DATEPART(YEAR,Sage)) AS age 
FROM student 
WHERE  CONVERT(CHAR(11),DATEPART(YEAR,Sage))='1981'; 

-- 改成19歲的人的名單
SELECT sname FROM student WHERE sage = 19;

-- 32、查詢每門課程的平均成績，結果按平均成績升序排列，平均成績相同時，按課程號降序排列
SELECT cid 課程號, AVG(score) 平均成績 FROM sc GROUP BY cid ORDER BY AVG(score), cid DESC;

-- 33、查詢平均成績大於75的所有學生的學號、姓名和平均成績
SELECT s.sid, sname, AVG(score) FROM student s, sc WHERE s.sid = sc.sid GROUP BY s.sid HAVING AVG(score) > 75;

-- 34、查詢課程名稱為“數學”，且分數低於60的學生姓名和分數
SELECT sname, score FROM student s, course c, sc WHERE s.sid = sc.sid AND c.cid = sc.cid AND cname='數學' AND score < 60;

-- 35、查詢所有學生的選課情況；
SELECT s.sid, sc.cid, s.sname, c.cname FROM student s, course c, sc WHERE s.sid = sc.sid AND c.cid = sc.cid;

-- 36、查詢任何一門課程成績在70分以上的姓名、課程名稱和分數；
SELECT s.sname, c.cname, score FROM student s, course c ,sc WHERE s.sid = sc.sid AND c.cid = sc.cid AND score > 70;

-- 37、查詢不及格的課程，並按課程號從大到小排列
SELECT s.sname, c.cid, c.cname, score FROM student s, course c, sc WHERE s.sid = sc.sid AND c.cid = sc.cid AND score < 60 ORDER BY cid DESC;

-- 38、查詢課程編號為02且課程成績在80分以上的學生的學號和姓名；
SELECT s.sid, s.sname FROM student s, sc WHERE s.sid = sc.sid AND score > 80 AND sc.cid=02;

-- 39、求選了課程的學生人數
SELECT COUNT(a.s) 選了課程的人數 FROM (SELECT COUNT(sid) s FROM sc GROUP BY sid) a;	-- 去除了重複的學生

SELECT COUNT(*) FROM sc;	-- 不去除重複學生

-- 40、查詢選修“葉平”老師所授課程的學生中，成績最高的學生姓名及其成績
SELECT sname, MAX(score) FROM student s, course c, teacher t, sc WHERE s.sid = sc.sid AND c.cid = sc.cid AND c.tid = t.tid AND tname = '張三';

-- 41、查詢各個課程及相應的選修人數
SELECT cid, COUNT(*) FROM sc GROUP BY cid;

-- 42、查詢不同課程成績相同的學生的學號、課程號、學生成績
SELECT sid, cid, score FROM sc WHERE score IN (SELECT score FROM sc GROUP BY score HAVING COUNT(score) >= 2) ORDER BY score;  -- 所有人之間對比

SELECT DISTINCT A.Sid,B.score FROM SC A ,SC B WHERE A.Score=B.Score AND A.Cid <>B.Cid ;  -- 單人成績對比

-- 43、查詢每門課程成績最好的前兩名
SELECT sid 學號, cid 課程ID, score 成績 FROM sc WHERE cid = 1 ORDER BY score DESC LIMIT 0,2;
SELECT sid 學號, cid 課程ID, score 成績 FROM sc WHERE cid = 2 ORDER BY score DESC LIMIT 0,2;
SELECT sid 學號, cid 課程ID, score 成績 FROM sc WHERE cid = 3 ORDER BY score DESC LIMIT 0,2;

-- 44、統計每門課程的學生選修人數（超過7人的課程才統計）。要求輸出課程號和選修人數，查詢結果按人數降序排列，若人數相同，按課程號升序排列
SELECT cid 課程ID, COUNT(*) 人數 FROM sc GROUP BY cid HAVING COUNT(*) >7 ORDER BY 人數, 課程ID DESC;

-- 45、檢索至少選修兩門課程的學生學號
SELECT sid FROM sc GROUP BY sid HAVING COUNT(sid) >=2;

-- 46、查詢全部學生都選修的課程的課程號和課程名
SELECT c.cid, c.cname,COUNT(sc.sid) FROM course c, sc WHERE c.cid = sc.cid GROUP BY c.cid HAVING COUNT(sc.sid) = (SELECT COUNT(*) FROM student);

-- 47、查詢沒學過“王五”老師講授的任一門課程的學生姓名
SELECT s1.sname FROM student s1 WHERE s1.sname NOT IN(
SELECT s.sname FROM student s, course c, teacher t, sc WHERE s.sid = sc.sid AND c.cid = sc.cid AND c.tid = t.tid AND t.tname = '王五');

-- 48、查詢兩門以上不及格課程的同學的學號及其平均成績
SELECT sid, AVG(score) FROM sc WHERE sid IN (SELECT sid FROM sc WHERE score < 60 GROUP BY sid HAVING COUNT(*)>=2);

-- 49、檢索“01”課程分數小於60，按分數降序排列的同學學號
SELECT sid, score FROM sc WHERE cid = 01 AND score < 60 ORDER BY score DESC;

-- 50、刪除“02”同學的“01”課程的成績
DELETE FROM sc WHERE sid = 02 AND cid = 01;