MySQL50题

阿里云国内75折回扣微信号：monov8

阿里云国际，腾讯云国际，低至75折。AWS 93折免费开户实名账号代冲值优惠多多微信号：monov8 飞机：@monov6

四张表

1.学生表 Students_id,s_name,s_birth,s_sex)

2.课程表Course(c_id,c_name,t_id)

3.教师表Teachert_idt_name)

4.成绩表Score(s_id,c_id,s_score)

建表语句

创建学生表并且往表中插入语句

CREATE TABLE `student` (
	`id` INT(11) NOT NULL AUTO_INCREMENT,
	`stu_name` VARCHAR(16) NOT NULL DEFAULT '0' COMMENT '学生姓名',
	`stu_age` VARCHAR(50) NOT NULL DEFAULT '0' COMMENT '学生年龄',
	`stu_sex` VARCHAR(50) NULL DEFAULT NULL COMMENT '性别1男2女',
	PRIMARY KEY (`id`)
)
COMMENT='学生表';

INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (1, '赵雷', '1990-01-01', '男');
INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (2, '钱电', '1990-12-21', '男');
INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (3, '孙风', '1990-05-20', '男');
INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (4, '李云', '1990-08-06', '男');
INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (5, '周梅', '1991-12-01', '女');
INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (6, '吴兰', '1992-03-01', '女');
INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (7, '郑竹', '1989-07-01', '女');
INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (8, '王菊', '1990-01-20', '女');
INSERT INTO `student` (`id`, `stu_name`, `stu_age`, `stu_sex`) VALUES (9, '冯丽', '1990-01-26', '女');

创建课程表并且插入数据

CREATE TABLE `course` (
	`id` INT(11) NOT NULL AUTO_INCREMENT,
	`course_name` VARCHAR(50) NULL DEFAULT '0' COMMENT '课程名称',
	`t_id` INT(11) NULL DEFAULT '0' COMMENT '教师id',
	PRIMARY KEY (`id`)
)
COMMENT='课程表'
COLLATE='utf8_general_ci';

INSERT INTO `course` (`id`, `course_name`, `t_id`) VALUES (1, '语文', 2);
INSERT INTO `course` (`id`, `course_name`, `t_id`) VALUES (2, '数学', 1);
INSERT INTO `course` (`id`, `course_name`, `t_id`) VALUES (3, '英语', 3);
INSERT INTO `course` (`id`, `course_name`, `t_id`) VALUES (4, '物理', 4);
INSERT INTO `course` (`id`, `course_name`, `t_id`) VALUES (5, '生物', 4);

创建成绩表并且插入数据

CREATE TABLE `score` (
	`student_id` INT(11) NULL DEFAULT NULL COMMENT '学生id',
	`course_id` INT(11) NULL DEFAULT NULL COMMENT '课程id',
	`score` INT(11) NULL DEFAULT NULL COMMENT '分数',
	UNIQUE INDEX `course_id_student_id` (`student_id`, `course_id`)
)
COMMENT='成绩表'
COLLATE='utf8_general_ci';

INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (1, 2, 90);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (8, 3, 89);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (5, 2, 87);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (3, 5, 86);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (1, 3, 86);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (3, 1, 81);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (3, 2, 80);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (3, 3, 80);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (2, 3, 80);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (5, 1, 76);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (5, 3, 69);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (2, 2, 60);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (6, 3, 59);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (6, 4, 59);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (4, 3, 59);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (4, 1, 50);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (2, 4, 50);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (6, 1, 31);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (4, 2, 30);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (9, 3, 30);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (7, 3, 30);
INSERT INTO `score` (`student_id`, `course_id`, `score`) VALUES (7, 4, 25);

创建教师表并且插入数据

CREATE TABLE `teacher` (
	`id` INT(11) NOT NULL AUTO_INCREMENT,
	`t_name` VARCHAR(50) NOT NULL COMMENT '教师名称',
	PRIMARY KEY (`id`)
)
COMMENT='教师表'
COLLATE='utf8_general_ci'
ENGINE=InnoDB
AUTO_INCREMENT=5
;

INSERT INTO `teacher` (`id`, `t_name`) VALUES (1, '张三');
INSERT INTO `teacher` (`id`, `t_name`) VALUES (2, '李四');
INSERT INTO `teacher` (`id`, `t_name`) VALUES (3, '王五');
INSERT INTO `teacher` (`id`, `t_name`) VALUES (4, '叶平');

题目1查询哪些学生的01这门课的成绩比02这门课成绩高

只用到一张表成绩表Score这张表里面有三个字段,s_id,c_id,s_score

考察自连接

都是score分数表一张给它起别名叫表a专门用来查01这门课程的分数另一张给它起别名叫表b专门用来查02这门课程的分

select *
from  score a
where  a.c_id='01'


select  *
from  score b
where  b.c_id='02'

现在连接两张表

SELECT  a.s_id,a.s_score course01,b.s_score course02
FROM   score a,score  b
WHERE  a.c_id='01' AND  b.c_id='02'  AND  a.s_id=b.s_id  AND a.s_score>b.s_score

题目2查询平均成绩大于等于60分的同学的学生编号和平均成绩

这道题显然直接告诉你最后结果需要呈现两列学生编号平均成绩

用到score这张表

主要可以学到group by进行分组

select   a.s_id,
         avg(a.s_score)  avg_s   
from    score  a
group  by  a.s_id

select   a.s_id,
         avg(a.s_score)  avg_s   
from    score  a
group  by  a.s_id
having   avg(a.s_score)>=60

如果还要查询出学生的姓名则还要连接学生表student这张表

select   a.s_id,
         avg(a.s_score)  avg_s   
         s.s_name
from    score  a,student  s
where   a.s_id=s.s_id
group  by    a.s_id
having   avg(a.s_score)>=60