mysql笔记: 查询

查询准备

CREATE DATABASE search;

use search;

# 学生表(student)：学号、姓名、性别、出生日期、班级

CREATE TABLE student(

sno varchar(20) primary key,

sname varchar(20) not null,

ssex varchar(10) not null,

sbirthday datetime,

class varchar(20)

) character set = utf8;

# 教师表(teacher)：编号、姓名、性别、出生日期、职称、所在部门

CREATE TABLE teacher(

tno varchar(20) primary key,

tname varchar(20) not null,

tsex varchar(10) not null,

tbirthday datetime,

prof varchar(20),

depart varchar(20) not null

) character set = utf8;

# 课程表(course)：课程号、课程名称、教师编号

CREATE TABLE course(

cno varchar(20) primary key,

cname varchar(20) not null,

tno varchar(20) not null,

foreign key(tno) references teacher(tno)

) character set = utf8;

# 成绩表(score)：学号、课程号、成绩

CREATE TABLE score(

sno varchar(20) not null,

cno varchar(20) not null,

degree decimal,

foreign key(sno) references student(sno),

foreign key(cno) references course(cno),

primary key(sno, cno)

) character set = utf8;

show tables;

# 向数据表中添加数据

# 添加学生信息

INSERT INTO student VALUES('101', '曾华', '男', '1977-09-01', '95033');

INSERT INTO student VALUES('102', '匡明', '男', '1975-10-02', '95031');

INSERT INTO student VALUES('103', '王丽', '女', '1976-01-23', '95033');

INSERT INTO student VALUES('104', '李军', '男', '1976-02-20', '95033');

INSERT INTO student VALUES('105', '王芳', '女', '1975-02-01', '95031');

INSERT INTO student VALUES('106', '陆君', '男', '1974-06-03', '95031');

INSERT INTO student VALUES('107', '王尼玛', '男', '1976-02-20', '95033');

INSERT INTO student VALUES('108', '张全蛋', '男', '1975-02-02', '95031');

INSERT INTO student VALUES('109', '赵铁柱', '男', '1974-06-03', '95031');

# 添加教师信息

INSERT INTO teacher VALUES('804', '李诚', '男', '1958-12-02', '副教授', '计算机系');

INSERT INTO teacher VALUES('856', '张旭', '男', '1969-03-12', '讲师', '电子工程系');

INSERT INTO teacher VALUES('825', '王萍', '女', '1972-05-05', '助教', '计算机系');

INSERT INTO teacher VALUES('831', '刘冰', '女', '1977-08-14', '助教', '电子工程系');

# 添加课程表

INSERT INTO course VALUES('3-105', '计算机导论', '825');

INSERT INTO course VALUES('3-245', '操作系统', '804');

INSERT INTO course VALUES('6-166', '数据电路', '856');

INSERT INTO course VALUES('9-888', '高等数学', '831');

# 分数表

INSERT INTO score VALUES('103', '3-245', '86');

INSERT INTO score VALUES('105', '3-245', '75');

INSERT INTO score VALUES('109', '3-245', '68');

INSERT INTO score VALUES('103', '3-105', '92');

INSERT INTO score VALUES('105', '3-105', '88');

INSERT INTO score VALUES('109', '3-105', '76');

INSERT INTO score VALUES('103', '6-166', '85');

INSERT INTO score VALUES('105', '6-166', '79');

INSERT INTO score VALUES('109', '6-166', '81');

INSERT INTO score VALUES('101', '3-105', '90');

INSERT INTO score VALUES('102', '3-105', '91');

INSERT INTO score VALUES('104', '3-105', '89');

查询练习

# 1、查询student表达所有记录

SELECT * FROM student;

# 2、查询student表中的所有记的的sname、ssex和class列

SELECT sname, ssex, class FROM student;

# 3、查询教师所有的单位即不重复的depart列

# distinct 排除重复

SELECT distinct depart FROM teacher;

# 4、查询score表中成绩在60-80之间的所有记录

# between 查询区间

SELECT * FROM score WHERE degree BETWEEN 60 AND 80;

# 预算符比较

SELECT * FROM score WHERE degree > 60 AND degree < 80;

# 5、查询score表中成绩为85、86或88的记录

# 在同一字段表示或关系的查询 IN

SELECT * FROM score WHERE degree IN(85, 86, 88);

# 6、查询student表中'95031'班或性别为'女'的同学记录

# 在不同字段表示或关系的查询 OR

SELECT * FROM student WHERE class='95031' OR ssex='女';

# 7、以class降序查询student表的所有记录

# 升序(asc)和降序(desc),默认是升序

SELECT * FROM student ORDER BY  class DESC;

# 8、以cno升序、degree降序查询score表的所有记录

SELECT * FROM score ORDER BY cno, degree DESC;

# 9、查询'95031'班的学生人数

# 统计 count

SELECT COUNT(*) FROM student WHERE class='95031';

# 10、查询score表中的最高分的学生号和课程号

# 复合子查询

SELECT sno, cno FROM score WHERE degree=(SELECT max(degree) FROM score);

# 11、查询每门课的平均成绩

# GROUP BY分组

SELECT cno, avg(degree) FROM score GROUP BY cno;

# 12、查询score中至少有2名学生选修的并以3开头的课程的平均分数

SELECT cno, avg(degree), count(*) FROM score GROUP BY cno HAVING count(cno) >= 2 and cno like '3%';

# 13、查询分数大于70小于98的sno列

SELECT sno, degree FROM score WHERE degree > 70 AND degree < 90;

# 14、查询所有学生的sname、cno 和 degree列

# 多表查询

SELECT sname, cno, degree FROM student, score WHERE student.sno = score.sno;

# 15、查询所有学生的sno、cname和degree列

SELECT sno, cname, degree FROM course, score WHERE course.cno = score.cno;

# 16、查询所有学生的sname、cname和degree列

SELECT sname, cname, degree FROM student, course, score WHERE student.sno=score.sno AND course.cno=score.cno;

# 17、查询'95031'班学生每门可的平均分

# 子查询 + 分组查询

SELECT cno, avg(degree) FROM score WHERE sno in (SELECT sno FROM student WHERE class='95031') GROUP BY cno;

# 18、查询选修'3-105'课程的成绩高于'109'号同学'3-105'成绩的所有同学记录

SELECT * FROM score WHERE cno = '3-105' AND degree > (SELECT degree FROM score WHERE sno='109' AND cno='3-105');

# 19、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 score WHERE degree > (SELECT degree FROM score WHERE sno='109' AND cno='3-105');

# 20、查询和学号为108、101的同学同年出生的所有学生的sno、sname和sbirthday列

# year函数与带关键字的子查询

SELECT * FROM student WHERE year(sbirthday) in (SELECT year(sbirthday) FROM student WHERE sno in(108, 101));

# 21、查询'张旭'教师任课的学生成绩。

# 多层嵌套查询

SELECT degree FROM score WHERE cno=(SELECT cno FROM course WHERE tno=(SELECT tno FROM teacher WHERE tname='张旭'));

# 22、查询选修某课程的同学人数多于5人的教师姓名。

# 多表查询

SELECT tname FROM teacher WHERE tno=(SELECT tno FROM course WHERE cno=(SELECT cno FROM score GROUP BY cno HAVING count(*) > 5));

# 23、查询95033班和95031班全体学生的记录。

# in表示或者关系

SELECT * FROM student WHERE class in('95033', '95031');

# 24、查询存在有85分以上成绩的课程cno;

SELECT cno, degree FROM score WHERE degree>85;

# 25、查询出'计算机系'教师所教课程的成绩表。

SELECT * FROM score WHERE cno in(SELECT cno FROM course WHERE tno in(SELECT tno FROM teacher WHERE depart='计算机系'));

# 26、查询'计算机系'与'电子工程系'不同职称教师的tname和prof。

# union 和 not in 的使用

SELECT * FROM teacher WHERE depart='计算机系' and prof not in(SELECT prof FROM teacher WHERE depart='电子工程系')

union

SELECT * FROM teacher WHERE depart='电子工程系' and prof not in(SELECT prof FROM teacher WHERE depart='计算机系');

# 27、查询选修编号'3-105'课程且成绩至少高于选修编号为'3-245'的同学的cno、sno和degree,并按degree从高到低次序排序。

# 至少？ 大于其中至少一个，any()

SELECT * FROM score WHERE cno='3-105' AND degree > any(SELECT degree FROM score WHERE cno='3-245') ORDER BY degree DESC;

# 28、查询选修编号为'3-105'且成绩高于选修编号为'3-245'课程的同学的cno、sno和degree。

# 且？ all()

SELECT * FROM score WHERE cno='3-105' AND degree > all(SELECT degree FROM score WHERE cno='3-245');

# 29、查询所有教师和同学的name、sex和birthday。

# 别名？ as

SELECT tname as name, tsex as sex, tbirthday as birthday FROM teacher

union

SELECT sname, ssex, sbirthday FROM student;

# 30、查询所有女教师和女同学的name、sex和birthday。

SELECT tname as name, tsex as sex, tbirthday as birthday FROM teacher WHERE tsex='女'

union

SELECT sname, ssex, sbirthday FROM student WHERE ssex='女';

# 31、查询成绩比该课程平均成绩低的同学的成绩表。

SELECT * FROM score a WHERE degree < (SELECT avg(degree) FROM score b WHERE a.cno=b.cno);

# 32、查询所有任课教师的tname和depart

SELECT tname, depart FROM teacher WHERE tno in(SELECT tno FROM course);

# 33、查询至少2名男生的班号

SELECT class FROM student WHERE ssex='男' GROUP BY class HAVING count(*) > 1;

# 34、查询student表中不姓'王'的同学记录。

# not like模糊查询取反

SELECT * FROM student WHERE sname not like '王%';

# 35、查询student表中每个学生的姓名和年龄

# 年龄 = 当前年份-出生年份

SELECT sname, year(now()) - year(sbirthday) as 'age' FROM student;

# 36、查询student表中最大和最小的sbirthday日期值。

# max min

SELECT max(sbirthday) as max, min(sbirthday) as min FROM student;

# 37、以班号和年龄从大到小的顺序查询student表中的全部记录

SELECT * FROM student ORDER BY class DESC, sbirthday DESC;

# 38、查询'男'教师及其所上的课程

SELECT * FROM course WHERE tno in(SELECT tno FROM teacher WHERE tsex='男');

# 39、查询最高分同学的sno、cno和degree列

SELECT * FROM score WHERE degree=(SELECT max(degree) FROM score);

SQL的四种连接查询

# 内连接：

# inner join 或 join

# 外连接：

# 1.左连接 left join 或者 left outer join

# 2.右连接 right join 或者 right outer join

# 3.完全外连接 full join 或者 full outer join

# 创建两个表

# Person表：id, name, cardid

CREATE TABLE person(

id int,

name varchar(20),

cardid int

) character set = utf8;

# Card表：id, name

CREATE TABLE card(

id int,

name varchar(20)

) character set = utf8;

INSERT INTO card VALUES(1, '饭卡');

INSERT INTO card VALUES(2, '建行卡');

INSERT INTO card VALUES(3, '农行卡');

INSERT INTO card VALUES(4, '工商卡');

INSERT INTO card VALUES(5, '邮政卡');

INSERT INTO person VALUES(1, '张三', 1);

INSERT INTO person VALUES(2, '李四', 3);

INSERT INTO person VALUES(3, '王五', 6);

# 这两张表并没有创建外键

# 1. inner join查询(内链接)

SELECT * FROM person inner join card on person.cardid = card.id;

# inner join 内联查询，其实就是两张表中的数据，通过某个字段相等，查询出相关数据记录，和join的效果一样

SELECT * FROM person join card on person.cardid = card.id;

# 2. left join查询(左外连接)

SELECT * FROM person left join card on person.cardid = card.id;

# 左外连接会将左边表里面的所有数据取出来，而右边的表数据，如果有相等的就显示，没有的就补null

# left join 等同于 left outer join，下面的结果是一样的

SELECT * FROM person left outer join card on person.cardid = card.id;

# 3. right join查询(右外连接)

SELECT * FROM person right join card on person.cardid = card.id;

# 右外连接会将右边表里面的所有数据取出来，而左边的表数据，如果有相等的就显示，没有的就补null

# 右外连接与左外连接正好相反

# right join 等同于 right outer join，下面的结果是一样的

SELECT * FROM person right outer join card on person.cardid = card.id;

# 4. mysql不支持 full join, 通过左右连接的union来完成

SELECT * FROM person left join card on person.cardid = card.id

union

SELECT * FROM person right join card on person.cardid = card.id;

本文禁止转载或摘编

--

--

--

分享到：

投诉或建议

评论