這50道查詢練習確實很經典，題是我在網上找的，做完後你的SQL編寫能力肯定有一個提升。發現問題的歡迎提出，有更好方法的，可以提出來大家共同學習。

---------建立資料庫、表、插入資料----------------------

-- 建表
-- 學生表
CREATE TABLE Student(
    s_id VARCHAR(20) COMMENT '學生編號',
    s_name VARCHAR(20) NOT NULL DEFAULT '' COMMENT '學生姓名',
    s_birth VARCHAR(20) NOT NULL DEFAULT '' COMMENT '出生年月',
    s_sex VARCHAR(10) NOT NULL DEFAULT '' COMMENT '學生性別',
    PRIMARY KEY(s_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT '學生表';
-- 課程表
CREATE TABLE Course(
    c_id  VARCHAR(20) COMMENT '課程編號',
    c_name VARCHAR(20) NOT NULL DEFAULT '' COMMENT '課程名稱',
    t_id VARCHAR(20) NOT NULL COMMENT '教師編號',
    PRIMARY KEY(c_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT '課程表';
-- 教師表
CREATE TABLE Teacher(
    t_id VARCHAR(20) COMMENT '教師編號',
    t_name VARCHAR(20) NOT NULL DEFAULT '' COMMENT '教師姓名',
    PRIMARY KEY(t_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT '教師表';
-- 成績表
CREATE TABLE Score(
    s_id VARCHAR(20) COMMENT '學生編號',
    c_id  VARCHAR(20) COMMENT '課程編號',
    s_score INT(3) COMMENT '分數',
    PRIMARY KEY(s_id,c_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT '成績表';

-- 插入學生表測試資料
insert into Student values('01' , '趙雷' , '1990-01-01' , '男');
insert into Student values('02' , '錢電' , '1990-12-21' , '男');
insert into Student values('03' , '孫風' , '1990-05-20' , '男');
insert into Student values('04' , '李雲' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吳蘭' , '1992-03-01' , '女');
insert into Student values('07' , '鄭竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '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');

-- 成績表測試資料
insert into Score values('01' , '01' , 80);
insert into Score values('01' , '02' , 90);
insert into Score values('01' , '03' , 99);
insert into Score values('02' , '01' , 70);
insert into Score values('02' , '02' , 60);
insert into Score values('02' , '03' , 80);
insert into Score values('03' , '01' , 80);
insert into Score values('03' , '02' , 80);
insert into Score values('03' , '03' , 80);
insert into Score values('04' , '01' , 50);
insert into Score values('04' , '02' , 30);
insert into Score values('04' , '03' , 20);
insert into Score values('05' , '01' , 76);
insert into Score values('05' , '02' , 87);
insert into Score values('06' , '01' , 31);
insert into Score values('06' , '03' , 34);
insert into Score values('07' , '02' , 89);
insert into Score values('07' , '03' , 98);

--------------------------------------------------

-- 1、查詢"01"課程比"02"課程成績高的學生的資訊及課程分數
SELECT
    a.*, b.s_score AS score1,
    c.s_score AS score2
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' OR c.c_id =NULL)
WHERE
    b.s_score > c.s_score ;

-- 2、查詢"01"課程比"02"課程成績低的學生的資訊及課程分數
SELECT
    a.*, b.s_score AS score1,
    c.s_score AS score2
FROM
    student a
LEFT JOIN score b ON a.s_id = b.s_id
AND (b.c_id = '01' OR b.c_id =NULL)
LEFT JOIN score c ON a.s_id = c.s_id
AND c.c_id = '02' 
WHERE
    b.s_score < c.s_score ;

-- 3、查詢平均成績大於等於60分的同學的學生編號和學生姓名和平均成績
SELECT
    a.s_id,
    a.s_name,
    ROUND(AVG(b.s_score), 1) AS 平均成績
FROM
    student a
LEFT JOIN score b ON a.s_id = b.s_id
GROUP BY
    a.s_id
HAVING
    AVG(b.s_score) >= 60;

-- 4、查詢平均成績小於60分的同學的學生編號和學生姓名和平均成績
-- (包括有成績的和無成績的)
-- 方法一：
SELECT
    a.s_id,
    a.s_name,
    ROUND(AVG(b.s_score), 1) AS 平均成績
FROM
    student a
LEFT JOIN score b ON a.s_id = b.s_id
GROUP BY
    a.s_id
HAVING
    AVG(b.s_score) < 60
OR
a.s_id NOT IN(SELECT DISTINCT a.s_id FROM student a JOIN score b WHERE a.s_id=b.s_id);

-- 方法二：
SELECT
    a.s_id,a.s_name,
    ROUND(AVG(b.s_score),2) AS avg_score
FROM
    student a
JOIN score b ON a.s_id = b.s_id
GROUP BY
    a.s_id
HAVING AVG(b.s_score) < 60
UNION
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、查詢所有同學的學生編號、學生姓名、選課總數、所有課程的總成績,並從高到低排序
SELECT
    a.s_id,
    a.s_name,
    COUNT(b.s_id) AS 選課總數 ,
    SUM(b.s_score) AS 總成績
FROM
    student a
LEFT JOIN score b
ON
    a.s_id = b.s_id
GROUP BY a.s_id
ORDER BY SUM(b.s_score) DESC;

-- 6、查詢"李"姓老師的數量 
SELECT COUNT(t_id) FROM teacher WHERE t_name LIKE '李%';

-- 7、查詢學過"張三"老師授課的同學的資訊 
#張三編號
SELECT t_id FROM teacher WHERE t_name = '張三'
#張三代課的課程編號
SELECT c_id FROM course WHERE t_id = (SELECT t_id FROM teacher WHERE t_name = '張三')
#學張三課程的學生編號
SELECT s_id FROM score WHERE c_id = (SELECT c_id FROM course WHERE t_id = (SELECT t_id FROM teacher WHERE t_name = '張三'))
-- 方法一：
SELECT *FROM student WHERE 
s_id IN (SELECT s_id FROM score WHERE 
c_id = (SELECT c_id FROM course WHERE
t_id = (SELECT t_id FROM teacher WHERE t_name = '張三'))
);

-- 方法二：
SELECT a.* FROM student a
JOIN score b ON a.s_id = b.s_id
WHERE 
b.c_id IN (SELECT c_id FROM course WHERE t_id = (SELECT t_id FROM teacher WHERE t_name = '張三'));

-- 8、查詢沒學過"張三"老師授課的同學的資訊 
-- 方法一：
SELECT *FROM student WHERE 
s_id NOT IN (SELECT s_id FROM score WHERE 
c_id = (SELECT c_id FROM course WHERE
t_id = (SELECT t_id FROM teacher WHERE t_name = '張三'))
);

-- 9、查詢學過編號為"01"並且也學過編號為"02"的課程的同學的資訊,及兩門課程成績
-- 方法一
SELECT
    a.*, b.s_score,
    c.s_score 
FROM
    student a
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';

-- 方法二：
SELECT
    a.*, b.s_score,
    c.s_score
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、查詢學過編號為"01"但是沒有學過編號為"02"的課程的同學的資訊
SELECT s_id FROM score  WHERE c_id = '01'
SELECT s_id FROM score  WHERE c_id = '02'

SELECT *FROM student a
WHERE
a.s_id IN (SELECT s_id FROM score  WHERE c_id = '01')
AND a.s_id NOT IN (SELECT s_id FROM score  WHERE c_id = '02');


-- 11、查詢沒有學全所有課程的同學的資訊 
SELECT s_id FROM score
GROUP BY s_id
HAVING COUNT(s_id) != 3

#方法一：
SELECT *FROM student WHERE s_id IN(
    SELECT s_id FROM score
    GROUP BY s_id
    HAVING COUNT(s_id) != 3
);

#方法二：
SELECT a.s_id FROM score a 
    JOIN score b ON a.s_id=b.s_id AND b.c_id='02'
    JOIN score c ON a.s_id=c.s_id AND c.c_id='03'
    WHERE a.c_id='01'

SELECT *FROM student d WHERE d.s_id IN(
    SELECT e.s_id FROM score e WHERE e.s_id NOT IN(
        SELECT a.s_id FROM score a 
            JOIN score b ON a.s_id=b.s_id AND b.c_id='02'
            JOIN score c ON a.s_id=c.s_id AND c.c_id='03'
            WHERE a.c_id='01')
);

-- 12、查詢至少有一門課與學號為"01"的同學所學相同的同學的資訊 

SELECT c_id FROM score WHERE s_id ='01'

SELECT DISTINCT s_id FROM score WHERE c_id IN (SELECT c_id FROM score WHERE s_id ='01')

SELECT * FROM student a
WHERE
a.s_id IN (SELECT DISTINCT b.s_id FROM score b WHERE 
b.c_id IN (SELECT c.c_id FROM score c WHERE c.s_id ='01')
);

-- 13、查詢和"01"號的同學學習的課程完全相同的其他同學的資訊 

SELECT * FROM student WHERE s_id IN(
    SELECT DISTINCT s_id FROM score WHERE s_id!='01' AND c_id IN (SELECT c_id FROM score WHERE s_id ='01') 
    GROUP BY s_id
    HAVING COUNT(1)=(SELECT COUNT(1) FROM score WHERE s_id='01')
)

-- 15、查詢兩門及其以上不及格課程的同學的學號，姓名及其平均成績 
SELECT s_id FROM score WHERE s_score<60 GROUP BY s_id HAVING COUNT(1) >= 2

SELECT
    a.s_id,
    a.s_name,
    ROUND(AVG(b.s_score), 1) AS 平均成績 
FROM
    student a
LEFT JOIN score b ON a.s_id = b.s_id
GROUP BY a.s_id
HAVING
a.s_id IN(SELECT s_id FROM score WHERE s_score<60 GROUP BY s_id HAVING COUNT(1) >= 2)


-- 16、檢索"01"課程分數小於60，按分數降序排列的學生資訊及01分數
-- 方法一：
SELECT
    a.*, b.s_score
FROM
    student a
LEFT JOIN score b ON a.s_id = b.s_id
WHERE
    b.c_id = '01'
AND b.s_score < 60
ORDER BY
    b.s_score DESC;

-- 方法二：
SELECT
    a.*, b.s_score
FROM
    student a,score b
WHERE
a.s_id = b.s_id AND b.c_id='01' AND b.s_score < 60
ORDER BY
    b.s_score DESC;

-- 方法三（有點瑕疵）：
SELECT
    a.*, b.s_score
FROM
    student a
LEFT JOIN score b ON a.s_id = b.s_id
AND    b.c_id = '01'
AND b.s_score < 60
ORDER BY
    b.s_score DESC;

-- 17、按平均成績從高到低顯示所有學生的所有課程的成績以及平均成績

-- 方法一（自連線）：
SELECT
 a.s_id,
(SELECT s_score FROM score WHERE s_id=a.s_id AND c_id='01') AS score1,
(SELECT s_score FROM score WHERE s_id=a.s_id AND c_id='02') AS score2,
(SELECT s_score FROM score WHERE s_id=a.s_id AND c_id='03') AS score3,
ROUND(avg(a.s_score), 2) AS 平均分
FROM score a
GROUP BY a.s_id
ORDER BY 平均分 DESC;

-- 方法二（自連線）：
SELECT 
 a.s_id,
 b.s_score,
 c.s_score,
 d.s_score,
 ROUND(avg(a.s_score), 2) AS 平均分
FROM
    score 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'
LEFT JOIN score d ON a.s_id = d.s_id AND d.c_id='03'
GROUP BY a.s_id
ORDER BY 平均分 DESC;

-- 18.查詢各科成績最高分、最低分和平均分：以如下形式顯示：課程ID，課程name，最高分，最低分，平均分，及格率，中等率，優良率，優秀率
-- 及格為>=60，中等為：70-80，優良為：80-90，優秀為：>=90

SELECT 
a.c_id,
MAX(a.s_score),
 MIN(a.s_score),
 AVG(a.s_score)
FROM
    score a
GROUP BY a.c_id;

-- 方法一：
SELECT
    a.c_id AS 課程ID,
    b.c_name AS 課程name,
    MAX(a.s_score) AS 最高分,
    MIN(a.s_score) AS 最低分,
    ROUND(AVG(a.s_score),2) AS 平均分,
  ROUND(100*(SUM(CASE WHEN a.s_score >= 60 THEN 1 ELSE 0 END) / COUNT(1)) , 2)  AS '及格率',
    ROUND(100*(SUM(CASE WHEN a.s_score >= 70 AND  a.s_score <80 THEN 1 ELSE 0 END) / COUNT(1)) , 2)  AS '中等率',
  ROUND(100*(SUM(CASE WHEN a.s_score >= 80 AND  a.s_score <90 THEN 1 ELSE 0 END) / COUNT(1)) , 2)  AS '優良率',
  ROUND(100*(SUM(CASE WHEN a.s_score >= 90 THEN 1 ELSE 0 END) / COUNT(1)) , 2)  AS '優秀率'
FROM
    score a
LEFT JOIN course b ON a.c_id = b.c_id
GROUP BY
    b.c_id;

-- 19、按各科成績進行排序，並顯示排名
-- mysql沒有rank順序函式
 select a.s_id,a.c_id,
        @i:
 
[email protected] +1 as i保留排名,
        @k:=(case when @score=a.s_score then @k else @i end) as rank不保留排名,
        @score:=a.s_score as score
    from (
        select s_id,c_id,s_score from score WHERE c_id='01' GROUP BY s_id,c_id,s_score ORDER BY s_score DESC
)a,(select @k:=0,@i:=0,@score:=0)s
    union
    select a.s_id,a.c_id,
        @i:
 
[email protected] +1 as i,
        @k:=(case when @score=a.s_score then @k else @i end) as rank,
        @score:=a.s_score as score
    from (
        select s_id,c_id,s_score from score WHERE c_id='02' GROUP BY s_id,c_id,s_score ORDER BY s_score DESC
)a,(select @k:=0,@i:=0,@score:=0)s
    union
    select a.s_id,a.c_id,
        @i:
 
[email protected] +1 as i,
        @k:=(case when @score=a.s_score then @k else @i end) as rank,
        @score:=a.s_score as score
    from (
        select s_id,c_id,s_score from score WHERE c_id='03' GROUP BY s_id,c_id,s_score ORDER BY s_score DESC
)a,(select @k:=0,@i:=0,@score:=0)s

-- 20、查詢學生的總成績並進行排名
SELECT a.s_id,
    @i:[email protected]+1 AS i,
    @k:=(CASE WHEN @score=a.sum_score THEN @k ELSE @i END) AS rank,
    @score:=a.sum_score AS score
FROM (SELECT s_id,SUM(s_score) AS sum_score FROM score GROUP BY s_id ORDER BY sum_score DESC) AS a,
(SELECT @i:=0,@score:=0) AS b

-- 21、查詢不同老師所教不同課程平均分從高到低顯示 
SELECT
    a.t_name,
    b.c_id,
    b.c_name,
    ROUND(AVG(c.s_score) ,2) AS 平均分
FROM
    teacher a
LEFT JOIN course b ON a.t_id = b.t_id
LEFT JOIN score c ON b.c_id=c.c_id
GROUP BY c.c_id
ORDER BY AVG(c.s_score) DESC;

-- 22、查詢所有課程的成績第2名到第3名的學生資訊及該課程成績
SELECT c.*,d.s_name,d.s_birth,d.s_sex FROM 
(SELECT a.s_id,a.s_score,a.c_id,@i:[email protected]+1 AS 排名 FROM score a,(SELECT @i:=0)b WHERE a.c_id='01') c 
LEFT JOIN student d ON c.s_id=d.s_id
WHERE 排名 BETWEEN 2 AND 3
UNION
SELECT c.*,d.s_name,d.s_birth,d.s_sex FROM 
(SELECT a.s_id,a.s_score,a.c_id,@j:[email protected]+1 AS 排名 FROM score a,(SELECT @j:=0)b WHERE a.c_id='02') c 
LEFT JOIN student d ON c.s_id=d.s_id
WHERE 排名 BETWEEN 2 AND 3
UNION
SELECT c.*,d.s_name,d.s_birth,d.s_sex FROM 
(SELECT a.s_id,a.s_score,a.c_id,@k:[email protected]+1 AS 排名 FROM score a,(SELECT @k:=0)b WHERE a.c_id='03') c 
LEFT JOIN student d ON c.s_id=d.s_id
WHERE 排名 BETWEEN 2 AND 3;

-- 23、統計各科成績各分數段人數：課程編號,課程名稱,[100-85],[85-70],[70-60],[0-60]及所佔百分比
  
SELECT
    a.c_id AS 課程編號, a.c_name AS 課程名稱,
  c.`[100-85]的人數`, c.`[100-85]所佔百分比`,
    d.`[85-70]的人數`, d.`[85-70]所佔百分比`,
    e.`[70-60]的人數`, e.`[70-60]所佔百分比`,
    f.`[0-60]的人數`, f.`[0-60]所佔百分比`
FROM
    course a
LEFT JOIN score b ON a.c_id = b.c_id
LEFT JOIN
    (SELECT *,SUM(CASE WHEN s_score >85 AND s_score <=100 THEN 1 ELSE 0 END) AS '[100-85]的人數' ,
    ROUND(SUM(CASE WHEN s_score >85 AND s_score <=100 THEN 1 ELSE 0 END)/COUNT(1)*100,2) AS '[100-85]所佔百分比'
    FROM score GROUP BY c_id) c ON a.c_id=c.c_id
LEFT JOIN
    (SELECT*,SUM(CASE WHEN s_score >70 AND s_score <=85 THEN 1 ELSE 0 END) AS '[85-70]的人數' ,
    ROUND(SUM(CASE WHEN s_score >70 AND s_score <=85 THEN 1 ELSE 0 END)/COUNT(1)*100,2) AS '[85-70]所佔百分比'
    FROM score GROUP BY c_id) d ON a.c_id=d.c_id
LEFT JOIN
    (SELECT*,SUM(CASE WHEN s_score >60 AND s_score <=70 THEN 1 ELSE 0 END) AS '[70-60]的人數' ,
    ROUND(SUM(CASE WHEN s_score >60 AND s_score <=70 THEN 1 ELSE 0 END)/COUNT(1)*100,2) AS '[70-60]所佔百分比'
    FROM score GROUP BY c_id) e ON a.c_id=e.c_id
LEFT JOIN
    (SELECT *,SUM(CASE WHEN s_score >0 AND s_score <=60 THEN 1 ELSE 0 END) AS '[0-60]的人數' ,
    ROUND(SUM(CASE WHEN s_score >0 AND s_score <=60 THEN 1 ELSE 0 END)/COUNT(1)*100,2) AS '[0-60]所佔百分比'
    FROM score GROUP BY c_id) f ON a.c_id=f.c_id
GROUP BY a.c_id

-- 24、查詢學生平均成績及其名次 
SELECT
    b.s_id,
    @i:[email protected]+1 AS 相同分數的不同名次,
    @k:=(CASE WHEN @avg_s=b.avg_score THEN @k ELSE @i END) AS 相同分數的相同名次,
    @avg_s:=b.avg_score AS 平均成績
FROM
(SELECT
    a.s_id,
    ROUND(AVG(a.s_score), 2) AS avg_score
FROM
    score a
GROUP BY
    a.s_id
ORDER BY AVG(a.s_score) DESC) b,(SELECT @i:=0,@avg_s:=0,@k:=0) c


-- 24.1新增名次rank,（相同分數的相同名次，並列排名）
-- 上面24難以看出並列排名
SELECT
    b.s_id,    b.c_id,
    -- 順序一直在變大
    @i:[email protected]+1 AS 相同分數的不同名次,
  -- 只有在前後二次分數不同時才會使用順序號
    @k:=(CASE WHEN @s=b.s_score THEN @k ELSE @i END) AS 相同分數的相同名次,
    @s:=b.s_score AS 成績
FROM
(SELECT *FROM score  WHERE s_id='03' ORDER BY s_score DESC)b,
(SELECT @i:=0,@k:=0,@s:=0)c

-- 25、查詢各科成績前三名的記錄
-- 1.選出b表比a表成績大的所有組
-- 2.選出比當前id成績大的 小於三個的
-- SELECT  a.s_id,a.c_id,a.s_score FROM score a 
-- LEFT JOIN score b ON a.c_id=b.c_id AND a.s_score<b.s_score 
-- GROUP BY a.s_id,a.c_id,a.s_score 
-- HAVING COUNT(b.s_id)<3
-- ORDER BY a.c_id,a.s_score DESC

-- 26、查詢每門課程被選修的學生數 
SELECT c_id,COUNT(1) FROM  score GROUP BY c_id

-- 27、查詢出只有兩門課程的全部學生的學號和姓名 
-- 方法一：
SELECT a.s_id,a.s_name FROM student a 
LEFT JOIN score b ON a.s_id=b.s_id
GROUP BY a.s_id
HAVING COUNT(1)=2

-- 方法二：
SELECT a.s_id,a.s_name FROM student a WHERE a.s_id IN 
(SELECT s_id FROM score GROUP BY s_id HAVING COUNT(1)=2)

-- 28、查詢男生、女生人數 
SELECT s_sex,COUNT(1) FROM student GROUP BY s_sex

-- 29、查詢名字中含有"風"字的學生資訊
SELECT *FROM student WHERE s_name LIKE '%風%' 

-- 30、查詢同名同性學生名單，並統計同名人數 
SELECT a.s_name,a.s_sex,COUNT(1) AS 人數 FROM student a 
JOIN student b ON a.s_name=b.s_name AND a.s_sex=b.s_sex AND a.s_id!=b.s_id
GROUP BY a.s_name,a.s_sex

-- 31、查詢1990年出生的學生名單
-- 方法一
SELECT s_name FROM student WHERE YEAR(s_birth)='1990'
-- 方法二
SELECT s_name FROM student WHERE s_birth LIKE '1990%'

-- 32、查詢每門課程的平均成績，結果按平均成績降序排列，平均成績相同時，按課程編號升序排列
SELECT c_id,ROUND(avg(s_score),2)FROM score 
GROUP BY c_id
ORDER BY avg(s_score) DESC,c_id ASC 

-- 33、查詢平均成績大於等於85的所有學生的學號、姓名和平均成績 
SELECT a.s_id,a.s_name,ROUND(avg(b.s_score),2) AS 平均成績 FROM student a 
LEFT JOIN score b ON a.s_id=b.s_id
GROUP BY a.s_id
HAVING avg(b.s_score) >= 85

-- 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 a.s_name,b.s_score FROM student a 
LEFT JOIN score b ON a.s_id=b.s_id
WHERE c_id=(
SELECT c_id FROM course WHERE c_name='數學'
) AND b.s_score < 60

-- 35、查詢所有學生的課程及分數情況； 
-- 方法一：
SELECT a.s_id,a.s_name,b.s_score,c.s_score,d.s_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'
LEFT JOIN score d ON a.s_id=d.s_id AND d.c_id='03'
GROUP BY a.s_id

-- 方法二：
 SELECT a.s_id,a.s_name,
SUM(CASE c.c_name WHEN '語文' THEN b.s_score ELSE 0 END) AS '語文',
SUM(CASE c.c_name WHEN '數學' THEN b.s_score ELSE 0 END) AS '數學',
SUM(CASE c.c_name WHEN '英語' THEN b.s_score ELSE 0 END) AS '英語',
SUM(b.s_score) as  '總分'
FROM student a 
LEFT JOIN score b ON a.s_id = b.s_id 
LEFT JOIN course c ON b.c_id = c.c_id 
GROUP BY a.s_id,a.s_name

 -- 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 a.s_name,c.c_name,b.s_score FROM student a
LEFT JOIN score b ON a.s_id=b.s_id
LEFT JOIN course c ON b.c_id=c.c_id
HAVING b.s_score > 70

-- 37、查詢不及格的學生id,姓名，及其課程名稱，分數
SELECT a.s_id,a.s_name,c.c_name,b.s_score FROM student a 
LEFT JOIN score b ON a.s_id=b.s_id
LEFT JOIN course c ON b.c_id=c.c_id
WHERE b.s_score < 60


-- 38、查詢課程編號為01且課程成績在80分以上的學生的學號和姓名； 
SELECT b.s_id,b.s_name FROM score a
LEFT JOIN student b ON a.s_id=b.s_id
WHERE a.c_id='01' AND a.s_score>80

-- 39、求每門課程的學生人數 
SELECT c_id,COUNT(1) FROM score GROUP BY c_id


-- 40、查詢選修"張三"老師所授課程的學生中，成績最高的學生資訊及其成績

SELECT t_id FROM teacher a WHERE a.t_name='張三'

SELECT c_id FROM course b WHERE t_id=(SELECT t_id FROM teacher a WHERE a.t_name='張三')

SELECT c.*,d.s_score FROM student c
LEFT JOIN score d ON c.s_id=d.s_id AND d.c_id=
(SELECT c_id FROM course b WHERE t_id=(SELECT t_id FROM teacher a WHERE a.t_name='張三'))
HAVING  MAX(d.s_score)


-- 41、查詢不同課程成績相同的學生的學生編號、課程編號、學生成績 
SELECT DISTINCT a.s_id,a.c_id,a.s_score 
FROM score a,score b WHERE a.s_score=b.s_score AND a.c_id!=b.c_id

-- 42、查詢每門功課成績最好的前兩名 
-- 方法一
SELECT *FROM
(SELECT a.s_id,a.c_id,a.s_score, @i:[email protected]+1 as 排名 FROM score a,(SELECT @i:=0)b WHERE a.c_id='01' ORDER BY a.s_score DESC
) c
WHERE 排名 BETWEEN 1 AND 2
UNION
SELECT *FROM
(SELECT a.s_id,a.c_id,a.s_score, @j:[email protected]+1 as 排名 FROM score a,(SELECT @j:=0)b WHERE a.c_id='02' ORDER BY a.s_score DESC
) c
WHERE 排名 BETWEEN 1 AND 2
UNION
SELECT *FROM
(SELECT a.s_id,a.c_id,a.s_score, @k:[email protected]+1 as 排名 FROM score a,(SELECT @k:=0)b WHERE a.c_id='03' ORDER BY a.s_score DESC
) c
WHERE 排名 BETWEEN 1 AND 2

-- 方法二
-- SELECT a.s_id,a.c_id,a.s_score FROM score a
-- WHERE (SELECT COUNT(1) FROM score b WHERE b.c_id=a.c_id AND b.s_score>=a.s_score)<=2 ORDER BY a.c_id

-- 43、統計每門課程的學生選修人數（超過5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 c_id AS 課程號,COUNT(1) AS 選修人數 FROM score 
GROUP BY c_id 
HAVING COUNT(1)>5 
ORDER BY COUNT(1) DESC,c_id

-- 44、檢索至少選修兩門課程的學生學號 
SELECT s_id,COUNT(1) FROM score GROUP BY s_id HAVING COUNT(1)>=2


-- 45、查詢選修了全部課程的學生資訊 
SELECT COUNT(1) FROM course

SELECT b.* FROM score a
LEFT JOIN student b ON a.s_id=b.s_id
GROUP BY a.s_id 
HAVING COUNT(1)=(SELECT COUNT(1) FROM course)

-- 46、查詢各學生的年齡
 -- 按照出生日期來算，當前月日<出生年月的月日則，年齡減一
-- 方法一
SELECT s_id,s_birth,(DATE_FORMAT(NOW(),'%Y')-DATE_FORMAT(s_birth,'%Y'))-
(CASE WHEN DATE_FORMAT(NOW(),'%m%d')< DATE_FORMAT(s_birth,'%m%d') THEN 1 ELSE 0 END) AS age
FROM student

-- 47、查詢本週過生日的學生
-- 方法一
SELECT * FROM student WHERE WEEK(CURRENT_DATE)=WEEK(s_birth)
-- 方法二
SELECT * FROM student WHERE WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))=WEEK(s_birth)

-- 48、查詢下週過生日的學生
SELECT * FROM student WHERE WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))+1=WEEK(s_birth)

-- 49、查詢本月過生日的學生
SELECT * FROM student WHERE MONTH(NOW())=MONTH(s_birth)

-- 50、查詢下月過生日的學生
SELECT * FROM student WHERE MONTH(NOW())+1=MONTH(s_birth)

SELECT DATE_FORMAT(NOW(),'%Y')
SELECT DATE_FORMAT(NOW(),'%Y%m%d')