【持续更新】学习MySQL时遇到的问题

一、修改数据库表和表中的字段的编码格式.
修改表的编码格式：

ALTER TABLE `table` DEFAULT CHARACTER SET utf8;

修改字段的编码格式：

ALTER TABLE `tablename` CHANGE `字段名1` `字段名2` VARCHAR(36) CHARACTER SET utf8 NOT NULL;

修改一张表中所有字段的编码格式：

alter table `tablename` convert to character set utf8;

二、查询位于某一个范围内的数，可以用BETWEEN
三、SQL练习
建表如下：

CREATE TABLE students
(sno VARCHAR(3) NOT NULL, 
sname VARCHAR(4) NOT NULL,
ssex VARCHAR(2) NOT NULL, 
sbirthday DATETIME,
class VARCHAR(5))

CREATE TABLE courses
(cno VARCHAR(5) NOT NULL, 
cname VARCHAR(10) NOT NULL, 
tno VARCHAR(10) NOT NULL)

CREATE TABLE scores 
(sno VARCHAR(3) NOT NULL, 
cno VARCHAR(5) NOT NULL, 
degree NUMERIC(10, 1) NOT NULL) 

CREATE TABLE teachers 
(tno VARCHAR(3) NOT NULL, 
tname VARCHAR(4) NOT NULL, tsex VARCHAR(2) NOT NULL, 
tbirthday DATETIME NOT NULL, prof VARCHAR(6), 
depart VARCHAR(10) NOT NULL)

插入数据：

INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (108 ,'曾华' ,'男' ,'1977-09-01',95033);
INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (105 ,'匡明' ,'男' ,'1975-10-02',95031);
INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (107 ,'王丽' ,'女' ,'1976-01-23',95033);
INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (101 ,'李军' ,'男' ,'1976-02-20',95033);
INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (109 ,'王芳' ,'女' ,'1975-02-10',95031);
INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (103 ,'陆君' ,'男' ,'1974-06-03',95031);

INSERT INTO COURSES(CNO,CNAME,TNO)VALUES ('3-105' ,'计算机导论',825);
INSERT INTO COURSES(CNO,CNAME,TNO)VALUES ('3-245' ,'操作系统' ,804);
INSERT INTO COURSES(CNO,CNAME,TNO)VALUES ('6-166' ,'数据电路' ,856);
INSERT INTO COURSES(CNO,CNAME,TNO)VALUES ('9-888' ,'高等数学' ,100);

INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (103,'3-245',86);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (105,'3-245',75);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (109,'3-245',68);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (103,'3-105',92);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (105,'3-105',88);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (109,'3-105',76);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (101,'3-105',64);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (107,'3-105',91);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (108,'3-105',78);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (101,'6-166',85);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (107,'6-106',79);
INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (108,'6-166',81);

INSERT INTO TEACHERS(TNO,TNAME,TSEX,TBIRTHDAY,PROF,DEPART) VALUES (804,'李诚','男','1958-12-02','副教授','计算机系');
INSERT INTO TEACHERS(TNO,TNAME,TSEX,TBIRTHDAY,PROF,DEPART) VALUES (856,'张旭','男','1969-03-12','讲师','电子工程系');
INSERT INTO TEACHERS(TNO,TNAME,TSEX,TBIRTHDAY,PROF,DEPART) VALUES (825,'王萍','女','1972-05-05','助教','计算机系');
INSERT INTO TEACHERS(TNO,TNAME,TSEX,TBIRTHDAY,PROF,DEPART) VALUES (831,'刘冰','女','1977-08-14','助教','电子工程系');

1.查询Student表中的所有记录的sname、ssex和class列

SELECT sname,ssex,class FROM student;

2.查询教师所有的单位即不重复的depart列。

SELECT DISTINCT depart FROM teachers;

3.查询students表的所有记录

SELECT * FROM students;

4.查询Score表中成绩在60到80之间的所有记录。

SELECT * FROM scores WHERE degree BETWEEN 60 AND 80;

5.查询Score表中成绩为85，86或88的记录。

SELECT * FROM scores WHERE segree IN (85,86,88);

6.查询student表中“95031”班或性别为“女”的同学记录。

SELECT * FROM students WHRER class='95031' or ssex='女';

7.以Class降序查询Student表的所有记录。

SELECT * FROM `students` ORDER BY class DESC

8.以Cno升序、Degree降序查询Score表的所有记录。

SELECT * FROM Scores ORDER BY Cno,Degree DESC;

9.查询“95031”班的学生人数。

SELECT COUNT(1) AS StuNum FROM Students WHERE Class='95031';

10.查询Score表中的最高分的学生学号和课程号。

SELECT sno,cno FROM scores WHERE degree in (SELECT max(degree) FROM scores);

11.查询‘3-105’号课程的平均分。

SELECT AVG (degree) AS aveScore FROM scores WHERE cno = '3-105'

12.查询Score表中至少有5名学生选修的并以3开头的课程的平均分数。(HAVING)

SELECT Cno,AVG(Degree)
FROM Scores
WHERE Cno LIKE '3%'
GROUP BY Cno
HAVING COUNT(Sno) >= 5;

13.查询最低分大于70，最高分小于90的sno列。(HAVING)

SELECT sno 
FROM scores 
GROUP BY sno 
HAVING MAX(degree)<90 AND MIN(degree)>70

14.查询所有学生的Sname、Cno和Degree列。(INNER JOIN)

SELECT
  sname,
  cno,
  degree
FROM
  `students`
INNER JOIN
  scores ON(students.sno = scores.sno)
ORDER BY
  sname

15.查询所有学生的Sno、Cname和Degree列。

SELECT
  sno,
  cname,
  degree
FROM
  `scores`
INNER JOIN
  courses ON scores.cno = courses,
  cno
ORDER BY
  sno;

16.查询所有学生的Sname、Cname和Degree列。

SELECT
  sname,
  cname,
  degree
FROM
  `students`
INNER JOIN
  scores ON students.sno = scores.sno
INNER JOIN
  courses ON scores.cno = courses.cno
ORDER BY
  sname

17.查询“95033”班所选课程的平均分。

SELECT
  cname,
  AVG(degree)
FROM
  `students`
INNER JOIN
  scores ON students.sno = scores.sno
INNER JOIN
  courses ON scores.cno = courses.cno
WHERE
  class = '95033'
GROUP BY
  courses.cno
ORDER BY
  cname

18.查询选修“3-105”课程的成绩高于“109”号同学成绩的所有同学的记录

SELECT
  *
FROM
  students,
  scores
WHERE
  scores.Cno = '3-105' AND students.sno = scores.sno AND scores.degree >(
  SELECT
    degree
  FROM
    scores
  WHERE
    cno = '3-105' AND sno = '109'
)

19.查询score中选学一门以上课程的同学中分数为非最高分成绩的记录。

这里写代码片

20.查询成绩高于学号为“109”、课程号为“3-105”的成绩的所有记录。

SELECT
  *
FROM
  scores,
  students
WHERE
  scores.sno = students.sno AND degree >(
  SELECT
    degree
  FROM
    scores
  WHERE
    sno = '109' AND cno = '3-105'
)

21.查询和学号为107的同学同年出生的所有学生的Sno、Sname和Sbirthday列。

SELECT
  sno,
  sname,
  sbirthday
FROM
  students
WHERE YEAR
  (students.sbirthday) =(
  SELECT YEAR
    (sbirthday)
  FROM
    students
  WHERE
    sno = '107'
)

22.查询“张旭“教师任课的学生成绩。

SELECT
  sno,
  cno,
  degree
FROM
  scores
WHERE
  cno IN(
  SELECT
    cno
  FROM
    courses
  WHERE
    tno IN(
    SELECT
      tno
    FROM
      teachers
    WHERE
      tname = '张旭'
  )
)

23.查询选修某课程的同学人数多于5人的教师姓名。

SELECT
  tname
FROM
  teachers
WHERE
  tno IN(
  SELECT
    tno
  FROM
    courses
  WHERE
    cno IN(
    SELECT
      cno
    FROM
      scores
    GROUP BY
      cno
    HAVING COUNT
      (*) > 5
  )
)

24.查询95033班和95031班全体学生的记录。

SELECT
  *
FROM
  students
WHERE
  class IN('95033',
  '95011')
ORDER BY
  class

25.查询存在有85分以上成绩的课程Cno。

SELECT DISTINCT
  cno
FROM
  scores
WHERE
  degree > 80

26.查询出“计算机系“教师所教课程的成绩表。

SELECT
  *
FROM
  `scores`
WHERE
  cno IN(
  SELECT
    cno
  FROM
    courses
  WHERE
    tno IN(
    SELECT
      tno
    FROM
      teachers
    WHERE
      depart = '计算机系'
  )
)

27.查询“计算机系”与“电子工程系“不同职称的教师的Tname和Prof。

这里写代码片

【持续更新】学习MySQL时遇到的问题

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