大家都知道，在面試中有一個重要環節就是筆試，而筆試中有個重要的環節，就是sql語句！
可見sql語句，是我們找工作當中非常重要的知識點，很多小夥伴面對眾多的sql不知道如何選擇！
那麼好！
福利來了，大家找工作前，把這個sql語句練好，就沒問題了！
第一：創建表和表關係，並插入數據
注意：這裡的數據是少量的數據，大家可以多加一些，導入你最喜歡的三國人物數據就ok
--班級表--
CREATE TABLE class(
cid INT NOT NULL,
caption VARCHAR(10),
PRIMARY KEY(cid)
);
INSERT INTO class VALUES(1,"三年二班"),(2,"一年三班"),(3,"三年一班");
--老師表--
CREATE TABLE teacher(
tid INT NOT NULL,
tname VARCHAR(10),
PRIMARY KEY(tid)
);
INSERT INTO teacher VALUES(1,"曹老師"),(2,"劉老師"),(3,"孫老師");
--學生表--
CREATE TABLE student(
sid INT NOT NULL,
sname VARCHAR(10),
gender VARCHAR(10),
class_id INT,
PRIMARY KEY(sid),
FOREIGN KEY(class_id) REFERENCES class(cid)
);
INSERT INTO student VALUES(1,"大喬","女",1),(2,"小喬","女",1),(3,"關羽","男",2);
--課程--
CREATE TABLE course(
cid INT NOT NULL,
cname VARCHAR(10),
teacher_id INT,
PRIMARY KEY(cid),
FOREIGN KEY(teacher_id) REFERENCES teacher(tid)
);
INSERT INTO course VALUES(1,"騎馬",1),(2,"射箭",1),(3,"畫畫",2);
--成績表--
CREATE TABLE score(
sid INT NOT NULL,
student_id INT,
corse_id INT,
number INT,
PRIMARY KEY(sid),
FOREIGN KEY(student_id) REFERENCES student(sid),
FOREIGN KEY(corse_id) REFERENCES course(cid)
);
INSERT INTO score VALUES (1,1,1,60),(2,1,2,59),(3,2,2,100);
第二：按照如下條件，進行操作
1、自行創建測試數據
2、查詢“生物”課程比“物理”課程成績高的所有學生的學號；
3、查詢平均成績大於60分的同學的學號和平均成績；
4、查詢所有同學的學號、姓名、選課數、總成績；
5、查詢姓“李”的老師的個數；
6、查詢沒學過“葉平”老師課的同學的學號、姓名；
7、查詢學過“001”並且也學過編號“002”課程的同學的學號、姓名；
8、查詢學過“葉平”老師所教的所有課的同學的學號、姓名；
9、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；
10、查詢有課程成績小於60分的同學的學號、姓名；
11、查詢沒有學全所有課的同學的學號、姓名；
12、查詢至少有一門課與學號為“001”的同學所學相同的同學的學號和姓名；
13、查詢至少學過學號為“001”同學所選課程中任意一門課的其他同學學號和姓名；
14、查詢和“002”號的同學學習的課程完全相同的其他同學學號和姓名；
15、刪除學習“葉平”老師課的SC表記錄；
16、向SC表中插入一些記錄，這些記錄要求符合以下條件：①沒有上過編號“002”課程的同學學號；②插入“002”號課程的平均成績；
17、按平均成績從低到高顯示所有學生的“語文”、“數學”、“英語”三門的課程成績，按如下形式顯示： 學生ID,語文,數學,英語,有效課程數,有效平均分；
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；
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；
20、課程平均分從高到低顯示（現實任課老師）；
21、查詢各科成績前三名的記錄:(不考慮成績並列情況)
22、查詢每門課程被選修的學生數；
23、查詢出只選修了一門課程的全部學生的學號和姓名；
24、查詢男生、女生的人數；
25、查詢姓“張”的學生名單；
26、查詢同名同姓學生名單，並統計同名人數；
27、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；
28、查詢平均成績大於85的所有學生的學號、姓名和平均成績；
29、查詢課程名稱為“數學”，且分數低於60的學生姓名和分數；
30、查詢課程編號為003且課程成績在80分以上的學生的學號和姓名；
31、求選了課程的學生人數
32、查詢選修“楊豔”老師所授課程的學生中，成績最高的學生姓名及其成績；
33、查詢各個課程及相應的選修人數；
34、查詢不同課程但成績相同的學生的學號、課程號、學生成績；
35、查詢每門課程成績最好的前兩名；
36、檢索至少選修兩門課程的學生學號；
37、查詢全部學生都選修的課程的課程號和課程名；
38、查詢沒學過“葉平”老師講授的任一門課程的學生姓名；
39、查詢兩門以上不及格課程的同學的學號及其平均成績；
40、檢索“004”課程分數小於60，按分數降序排列的同學學號；
41、刪除“002”同學的“001”課程的成績；
第三：先自行完成上面的題目，然後再對比如下的sql，進行檢查！~
1、自行創建測試數據
2、查詢“生物”課程比“物理”課程成績高的所有學生的學號；
SELECT * FROM
(SELECT score.student_id,course.cname,score.num FROM score LEFT JOIN course on score.course_id=course.cid WHERE course.cname="生物") AS A
INNER JOIN
(SELECT score.student_id,course.cname,score.num FROM score LEFT JOIN course on score.course_id=course.cid WHERE course.cname="物理") AS B
on A.student_id = B.student_id WHERE A.num > B.num;
3、查詢平均成績大於60分的同學的學號和平均成績；
SELECT B.student_id,student.sname,B.s_num FROM (SELECT student_id,avg(num) AS s_num from score GROUP BY student_id HAVING s_num>60) as B
LEFT JOIN student on B.student_id = student.sid; 取前三： %ORDER BY s_num desc LIMIT 3;
4、查詢所有同學的學號、姓名、選課數、總成績；
SELECT score.student_id,student.sname,COUNT(score.course_id) AS courses,SUM(num) as T_Score FROM score
LEFT JOIN student on score.student_id=student.sid GROUP BY score.student_id;
5、查詢姓“李”的老師的個數；
SELECT * from teacher WHERE tname like "李%";
6、查詢沒學過“李平”老師課的同學的學號、姓名；
SELECT student.sid,student.sname FROM student WHERE student.sid NOT IN (
SELECT score.student_id FROM score LEFT JOIN course ON score.course_id = course.cid WHERE score.course_id IN (
SELECT course.cid FROM course LEFT JOIN teacher ON course.teacher_id = teacher.tid WHERE teacher.tname LIKE "李平%") GROUP BY score.student_id)
7、查詢學過“001”並且也學過編號“002”課程的同學的學號、姓名；
SELECT B.sid,B.sname FROM(
SELECTstudent.sid,score.course_id,student.sname FROM score
LEFT JOIN student ON score.student_id = student.sid WHERE score.course_id BETWEEN 1 AND 2) AS B
GROUP BY B.sid HAVING COUNT(B.course_id)=2;
8、查詢學過“葉平”老師所教的所有課的同學的學號、姓名；
SELECT student.sid,student.sname FROM score LEFT JOIN student ON score.student_id=student.sid WHERE score.course_id in
(SELECT course.cid FROM course LEFT JOIN teacher on course.teacher_id=teacher.tid WHERE tname LIKE "李平%")
GROUP BY student.sid HAVING COUNT(student_id)=2;
9、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 A.sid,A.sname,A.num as score_2,B.num as score_1 FROM
(SELECT student.sid,student.sname,score.num FROM score LEFT JOIN student on score.student_id=student.sid WHERE score.course_id=2) AS A
INNER JOIN
(SELECT student.sid,student.sname,score.num FROM score LEFT JOIN student on score.student_id=student.sid WHERE score.course_id=1) AS B
ON A.sid = B.sid WHERE A.num<b.num>
10、查詢有課程成績小於60分的同學的學號、姓名；
SELECT student.sid,student.sname FROM student WHERE sid IN
(SELECT score.student_id FROM score WHERE score.num<60 GROUP BY student_id);
11、查詢沒有學全所有課的同學的學號、姓名；
SELECT student.sid,student.sname FROM student WHERE sid in
(SELECT student_id FROM score GROUP BY student_id HAVING count(course_id)!=(SELECT COUNT(cid) FROM course));
12、查詢至少有一門課與學號為“001”的同學所學相同的同學的學號和姓名；
SELECT student.sid,student.sname FROM student where student.sid in
(SELECT score.student_id FROM score WHERE course_id in
(SELECT score.course_id FROM score WHERE student_id=1) and student_id !=1 GROUP BY student_id);
13、查詢至少學過學號為“001”同學所選課程中任意一門課的其他同學學號和姓名；
SELECT student.sid,student.sname FROM student where student.sid in
(SELECT score.student_id FROM score WHERE course_id in
(SELECT score.course_id FROM score WHERE student_id=1) and student_id !=1 GROUP BY student_id
having count(1) =(SELECT count(score.course_id) FROM score WHERE student_id=1));
14、查詢和“002”號的同學學習的課程完全相同的其他同學學號和姓名；
SELECT sid AS 學號,sname AS 姓名 FROM student WHERE sid IN(
SELECT student_id FROM score WHERE student_id IN (
SELECT student_id FROM score WHERE student_id!=2 GROUP BY student_id
HAVING COUNT(1)=(SELECT COUNT(1) FROM score WHERE student_id=2))
AND course_id in (SELECT course_id FROM score WHERE student_id=2)
GROUP BY student_id HAVING COUNT(1)=(SELECT COUNT(1) FROM score WHERE student_id=2))
15、刪除學習“葉平”老師課的SC表記錄；
DELETE FROM score WHERE course_id IN
(SELECT cid FROM course LEFT JOIN teacher on course.teacher_id=teacher.tid WHERE tname="李平老師")
16、向SC表中插入一些記錄，這些記錄要求符合以下條件：①沒有上過編號“002”課程的同學學號；②插入“002”號課程的平均成績；
1、INSERT into score(student_id,course_id,num)
SELECT student_id,2,(SELECT AVG(num) FROM score WHERE course_id=2) FROM score WHERE course_id!=2 group by student_id
--2、SELECT AVG(num) FROM score WHERE course_id=2 --
17、按平均成績從低到高顯示所有學生的“語文”、“數學”、“英語”三門的課程成績，按如下形式顯示： 學生ID,語文,數學,英語,有效課程數,有效平均分；
SELECT student_id AS 學生ID,
(SELECT num FROM score LEFT JOIN course on score.course_id=course.cid WHERE course.cname="語文" AND student_id=s1.student_id) AS 語文,
(SELECT num FROM score LEFT JOIN course on score.course_id=course.cid WHERE course.cname="數學" AND student_id=s1.student_id) AS 數學,
(SELECT num FROM score LEFT JOIN course on score.course_id=course.cid WHERE course.cname="英語" AND student_id=s1.student_id) AS 英語
FROM score as s1 GROUP BY student_id;
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 score.course_id AS 課程ID,course.cname as 課程名,MAX(num) as 最高分,MIN(num) as 最低分 FROM score
LEFT JOIN course ON score.course_id=course.cid GROUP BY course_id;
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；
平均分：
SELECT score.course_id AS 課程ID,course.cname as 課程名,AVG(num) AS 平均分 FROM score
LEFT JOIN course ON score.course_id=course.cid GROUP BY score.course_id ORDER BY 平均分 ASC;
及格率：
SELECT A.cid,A.cname,ROUND(B.s/A.ss*100,1)+% AS 及格率 FROM
(SELECT cid,cname,COUNT(course_id) AS ss FROM score LEFT JOIN course ON score.course_id=course.cid GROUP BY course_id) as A
INNER JOIN
(SELECT course_id,COUNT(num) as s FROM score WHERE score.num>60 GROUP BY course_id) as B ON A.cid=B.course_id ORDER BY 及格率 DESC;
整合：
SELECT x.課程ID,x.課程名,x.平均分,xx.及格率 FROM
(SELECT score.course_id AS 課程ID,course.cname as 課程名,AVG(num) AS 平均分 FROM score
LEFT JOIN course ON score.course_id=course.cid GROUP BY score.course_id ORDER BY 平均分 ASC) AS x
LEFT JOIN
(SELECT A.cid,A.cname,ROUND(B.s/A.ss*100,1) AS 及格率 FROM
(SELECT cid,cname,COUNT(course_id) AS ss FROM score LEFT JOIN course ON score.course_id=course.cid GROUP BY course_id) as A
INNER JOIN
(SELECT course_id,COUNT(num) as s FROM score WHERE score.num>60 GROUP BY course_id) as B ON A.cid=B.course_id ORDER BY 及格率 DESC) AS xx
ON x.課程ID=xx.cid
標準：
SELECT course_id,AVG(num) AS 平均分,ROUND(sum(CASE WHEN num<60 then 0 ELSE 1 END)/sum(1)*100,1) AS 及格率
FROM score GROUP BY course_id ORDER BY 平均分 ASC,及格率 DESC;
20、課程平均分從高到低顯示（現實任課老師）；
SELECT course.cname,teacher.tname,xxx.平均分 FROM course
LEFT JOIN teacher ON course.teacher_id=teacher.tid
LEFT JOIN (SELECT course_id,AVG(num) AS 平均分 FROM score GROUP BY course_id) AS xxx ON xxx.course_id=course.cid
ORDER BY xxx.平均分 DESC
21、查詢各科成績前三名的記錄:(不考慮成績並列情況)
SELECT s1.cid AS 課程ID,s1.cname AS 課程,
(SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 0,1) AS 第一,
(SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 1,1) AS 第二,
(SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 2,1) AS 第三
FROM course AS s1
22、查詢每門課程被選修的學生數；
SELECT course.cid AS 課程ID,course.cname AS 課程名,COUNT(1) AS 學生數 FROM score
LEFT JOIN course ON score.course_id=course.cid GROUP BY score.course_id;
23、查詢出只選修了一門課程的全部學生的學號和姓名；
SELECT student.sid AS 學號,student.sname AS 姓名 FROM student
WHERE sid IN (SELECT student_id FROM score GROUP BY student_id HAVING count(1)=1)
24、查詢男生、女生的人數；
SELECT gender AS 性別,COUNT(1) AS 人數 FROM student GROUP BY gender;
25、查詢姓“張”的學生名單；
SELECT * FROM student WHERE sname LIKE "張%"
26、查詢同名同姓學生名單，並統計同名人數；
SELECT sname As 姓名,COUNT(1) AS 人數 FROM student GROUP BY sname;
27、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
course.cid AS 課程ID,
course.cname AS 課程名,
AVG(IF(ISNULL(num),0,score.num)) AS 平均分
FROM score LEFT JOIN course ON score.course_id = course.cid
GROUP BY score.course_id ORDER BY 平均分 ASC,課程ID DESC;
28、查詢平均成績大於85的所有學生的學號、姓名和平均成績；
SELECT student.sid AS 學號,student.sname AS 姓名,AVG(if(isnull(num),0,score.num)) AS 平均分
FROM score LEFT JOIN student ON score.student_id=student.sid
GROUP BY score.student_id HAVING 平均分>85;
29、查詢課程名稱為“數學”，且分數低於60的學生姓名和分數；
SELECT student.sid AS 學號,student.sname AS 姓名,score.num AS 成績 FROM score
LEFT JOIN course ON score.course_id=course.cid
LEFT JOIN student ON score.student_id= student.sid
WHERE course.cname="數學" AND score.num<60；
30、查詢課程編號為003且課程成績在80分以上的學生的學號和姓名；
SELECT student.sid AS 學號,student.sname AS 姓名 FROM student WHERE sid IN
(SELECT student_id FROM score WHERE score.course_id =3 AND num > 80)
31、求選了課程的學生人數
SELECT COUNT(A.student_id) AS 總人數
FROM (SELECT student_id FROM score GROUP BY student_id) AS A
SELECT COUNT(DISTINCT student_id) AS 總人數 FROM score;
32、查詢選修“楊豔”老師(這個老師沒有，就以張磊老師舉例)所授課程的學生中，成績最高的學生姓名及其成績；
SELECT student.sid AS 學號,student.sname AS 姓名,num AS 成績 FROM score
LEFT JOIN course ON score.course_id=course.cid
LEFT JOIN student ON score.student_id=student.sid
LEFT JOIN teacher ON course.teacher_id=teacher.tid
WHERE teacher.tname = "張磊老師" ORDER BY num DESC LIMIT 1;
33、查詢各個課程及相應的選修人數；
SELECT course_id AS ID,course.cname AS 課程,count(1) AS 人數 FROM score
LEFT JOIN course ON score.course_id=course.cid GROUP BY course_id
34、查詢不同課程但成績相同的學生的學號、課程號、學生成績；
SELECT DISTINCT s1.student_id,s1.course_id,s1.num FROM score AS s1,score AS s2
WHERE s1.student_id != s2.student_id AND s1.course_id!=s2.course_id AND s1.num=s2.num
35、查詢每門課程成績最好的前兩名；
SELECT cid AS 課程ID,cname AS 課程,
(SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 0,1) AS 第一,
(SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 1,1) AS 第二
FROM course AS s1
36、檢索至少選修兩門課程的學生學號；
SELECT student_id FROM score GROUP BY student_id HAVING count(course_id)>=2
37、查詢全部學生都選修的課程的課程號和課程名；
SELECT course.cid AS 課程號,course.cname AS 課程名 FROM score
LEFT JOIN course ON score.course_id=course.cid GROUP BY score.course_id
HAVING COUNT(student_id)=(SELECT COUNT(sid) FROM student)
38、查詢沒學過“李平”老師講授的任一門課程的學生姓名；
SELECT student.sid,student.sname FROM student
WHERE student.sid not IN (SELECT student_id FROM score
WHERE course_id IN(SELECT cid FROM course
LEFT JOIN teacher ON course.teacher_id=teacher.tid
WHERE teacher.tname="李平老師" ) GROUP BY student_id)
39、查詢兩門以上不及格課程的同學的學號及其平均成績；
SELECT score.student_id AS 學號,student.sname AS 姓名,
(SELECT AVG(if(ISNULL(A.num),0,A.num)) FROM score AS A
WHERE A.student_id IN (SELECT student_id FROM score WHERE num<60
GROUP BY student_id HAVING COUNT(1)>=2)) AS 平均成績
FROM score LEFT JOIN student ON score.student_id=student.sid
WHERE num<60 GROUP BY student_id HAVING COUNT(1)>2
標準：
SELECT student_id AS 學號,sname AS 姓名,AVG(num) AS 平均成績 FROM score
LEFT JOIN student ON score.student_id=student.sid
WHERE student_id IN (SELECT student_id FROM score
WHERE num<60 GROUP BY student_id HAVING COUNT(1)>=2)
GROUP BY student_id
40、檢索“004”課程分數小於60，按分數降序排列的同學學號；
SELECT student_id,num FROM score
WHERE score.course_id=4 AND num <60 ORDER BY num ASC
41、刪除“002”同學的“001”課程的成績；
delete from score where student_id=2 and corse_id=1;
/<b.num>
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