數據庫相關

1.數據庫操做

CREATE DATABASE 數據庫名 charset utf8;
1 查看數據庫
show databases;
show create database db1;
select database();

2 選擇數據庫
USE 數據庫名

3 刪除數據庫
DROP DATABASE 數據庫名;

4 修改數據庫
alter database db1 charset utf8;

2.表操做

示例：
1. 修改存儲引擎
mysql> alter table service 
    -> engine=innodb;

2. 添加字段
mysql> alter table student10
    -> add name varchar(20) not null,
    -> add age int(3) not null default 22;
    
mysql> alter table student10
    -> add stu_num varchar(10) not null after name;                //添加name字段以後

mysql> alter table student10                        
    -> add sex enum('male','female') default 'male' first;          //添加到最前面

3. 刪除字段
mysql> alter table student10
    -> drop sex;

mysql> alter table service
    -> drop mac;

4. 修改字段類型modify
mysql> alter table student10
    -> modify age int(3);
mysql> alter table student10
    -> modify id int(11) not null primary key auto_increment;    //修改成主鍵

5. 增長約束（針對已有的主鍵增長auto_increment）
mysql> alter table student10 modify id int(11) not null primary key auto_increment;
ERROR 1068 (42000): Multiple primary key defined

mysql> alter table student10 modify id int(11) not null auto_increment;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

6. 對已經存在的表增長複合主鍵
mysql> alter table service2
    -> add primary key(host_ip,port);        

7. 增長主鍵
mysql> alter table student1
    -> modify name varchar(10) not null primary key;

8. 增長主鍵和自動增加
mysql> alter table student1
    -> modify id int not null primary key auto_increment;

9. 刪除主鍵
a. 刪除自增約束
mysql> alter table student10 modify id int(11) not null; 

b. 刪除主鍵
mysql> alter table student10                                 
    -> drop primary key;

DROP TABLE 表名;

3.數據操做

插入

1. 插入完整數據（順序插入）
    語法一：
    INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES(值1,值2,值3…值n);

    語法二：
    INSERT INTO 表名 VALUES (值1,值2,值3…值n);

2. 指定字段插入數據
    語法：
    INSERT INTO 表名(字段1,字段2,字段3…) VALUES (值1,值2,值3…);

3. 插入多條記錄
    語法：
    INSERT INTO 表名 VALUES
        (值1,值2,值3…值n),
        (值1,值2,值3…值n),
        (值1,值2,值3…值n);
        
4. 插入查詢結果
    語法：
    INSERT INTO 表名(字段1,字段2,字段3…字段n) 
                    SELECT (字段1,字段2,字段3…字段n) FROM 表2
                    WHERE …;

更新

語法：
    UPDATE 表名 SET
        字段1=值1,
        字段2=值2,
        WHERE CONDITION;

示例：
    UPDATE mysql.user SET password=password(‘123’) 
        where user=’root’ and host=’localhost’;

刪除

語法：
    DELETE FROM 表名 
        WHERE CONITION;

示例：
    DELETE FROM mysql.user 
        WHERE password=’’;

練習：
    更新MySQL root用戶密碼爲123
    刪除除從本地登陸的root用戶之外的全部用戶

導出現有數據庫數據：

• mysqldump -u用戶名 -p密碼 數據庫名稱 >導出文件路徑           # 結構+數據
• mysqldump -u用戶名 -p密碼 -d 數據庫名稱 >導出文件路徑       # 結構 

導入現有數據庫數據：

• mysqldump -uroot -p密碼  數據庫名稱 < 文件路徑  

1、表關係

請建立以下表，並建立相關約束

1.建立表
create table class(
	cid int auto_increment primary key,
	caption char(10)
)engine=innodb default charset=utf8;
insert into class(caption) values('三年二班'),('一年三班'),('三年一班');


create table student(
	sid int auto_increment primary key,
	sname char(10),
	gender char(10),
	class_id int,
	constraint fk_class foreign key (class_id) references class(cid)
)engine=innodb default charset=utf8;
insert into student(sname,gender,class_id) values('鋼彈','女',1),('鐵錘','女',2),('山炮','男',2);


create table teacher(
	tid int auto_increment primary key,
	tname char(10)
)engine=innodb default charset=utf8;
insert into teacher(tname) values('波多'),('蒼空'),('飯島');


create table course(
	cid int auto_increment primary key,
	cname char(10),
	tearch_id int,
	constraint fk_teacher foreign key (tearch_id) references teacher(tid)
)engine=innodb default charset=utf8;
insert into course(cname,tearch_id) values('生物',1),('體育',1),('物理',2);


create table score(
	sid int auto_increment primary key,
	student_id int,
	corse_id int,
	number int,
	unique score_index (student_id,corse_id),
	constraint fk_student foreign key (student_id) references student(sid),
	constraint fk_corse foreign key (corse_id) references course(cid)
)engine=innodb default charset=utf8;
insert into score(student_id,corse_id,number) values(1,1,60),(1,2,59),(2,2,100);

下面建立的表內容比較多，用於後面的練習題使用。

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 50624
 Source Host           : localhost
 Source Database       : sqlexam

 Target Server Type    : MySQL
 Target Server Version : 50624
 File Encoding         : utf-8

 Date: 10/21/2016 06:46:46 AM
*/

SET NAMES utf8;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
--  Table structure for `class`
-- ----------------------------
DROP TABLE IF EXISTS `class`;
CREATE TABLE `class` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `caption` varchar(32) NOT NULL,
  PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `class`
-- ----------------------------
BEGIN;
INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');
COMMIT;

-- ----------------------------
--  Table structure for `course`
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `cname` varchar(32) NOT NULL,
  `teacher_id` int(11) NOT NULL,
  PRIMARY KEY (`cid`),
  KEY `fk_course_teacher` (`teacher_id`),
  CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `course`
-- ----------------------------
BEGIN;
INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '體育', '3'), ('4', '美術', '2');
COMMIT;

-- ----------------------------
--  Table structure for `score`
-- ----------------------------
DROP TABLE IF EXISTS `score`;
CREATE TABLE `score` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `student_id` int(11) NOT NULL,
  `course_id` int(11) NOT NULL,
  `num` int(11) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_score_student` (`student_id`),
  KEY `fk_score_course` (`course_id`),
  CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
  CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `score`
-- ----------------------------
BEGIN;
INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87');
COMMIT;

-- ----------------------------
--  Table structure for `student`
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `gender` char(1) NOT NULL,
  `class_id` int(11) NOT NULL,
  `sname` varchar(32) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_class` (`class_id`),
  CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `student`
-- ----------------------------
BEGIN;
INSERT INTO `student` VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '鋼蛋'), ('3', '男', '1', '張三'), ('4', '男', '1', '張一'), ('5', '女', '1', '張二'), ('6', '男', '1', '張四'), ('7', '女', '2', '鐵錘'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '劉三'), ('14', '男', '3', '劉一'), ('15', '女', '3', '劉二'), ('16', '男', '3', '劉四');
COMMIT;

-- ----------------------------
--  Table structure for `teacher`
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
  `tid` int(11) NOT NULL AUTO_INCREMENT,
  `tname` varchar(32) NOT NULL,
  PRIMARY KEY (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `teacher`
-- ----------------------------
BEGIN;
INSERT INTO `teacher` VALUES ('1', '張磊老師'), ('2', '李平老師'), ('3', '劉海燕老師'), ('4', '朱雲海老師'), ('5', '李傑老師');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

表結構和數據

上述表均是在Navicat建立的。

 

二、查詢「生物」課程比「物理」課程成績高的全部學生的學號；
思路：
    獲取全部有生物課程的人（學號，成績） - 臨時表
    獲取全部有物理課程的人（學號，成績） - 臨時表
    根據【學號】鏈接兩個臨時表：
        學號  物理成績   生物成績
 
    而後再進行篩選
 
        select A.student_id,sw,ty from
 
        (select student_id,num as sw from score left join course on score.course_id = course.cid where course.cname = '生物') as A
 
        left join
 
        (select student_id,num  as ty from score left join course on score.course_id = course.cid where course.cname = '體育') as B
 
        on A.student_id = B.student_id where sw > if(isnull(ty),0,ty);
 
三、查詢平均成績大於60分的同窗的學號和平均成績；
    思路：
        根據學生分組，使用avg獲取平均值，經過having對avg進行篩選
 
        select student_id,avg(num) from score group by student_id having avg(num) > 60
 
四、查詢全部同窗的學號、姓名、選課數、總成績；
 
    select score.student_id,sum(score.num),count(score.student_id),student.sname
    from
        score left join student on score.student_id = student.sid  
    group by score.student_id
 
五、查詢姓「李」的老師的個數；
    select count(tid) from teacher where tname like '李%'
 
    select count(1) from (select tid from teacher where tname like '李%') as B
 
六、查詢沒學過「葉平」老師課的同窗的學號、姓名；
    思路：
        先查到「李平老師」老師教的全部課ID
        獲取選過課的全部學生ID
        學生表中篩選
    select * from student where sid not in (
        select DISTINCT student_id from score where score.course_id in (
            select cid from course left join teacher on course.teacher_id = teacher.tid where tname = '李平老師'
        )
    )
 
七、查詢學過「001」而且也學過編號「002」課程的同窗的學號、姓名；
    思路：
        先查到既選擇001又選擇002課程的全部同窗
        根據學生進行分組，若是學生數量等於2表示，兩門均已選擇
 
    select student_id,sname from
 
    (select student_id,course_id from score where course_id = 1 or course_id = 2) as B
      
    left join student on B.student_id = student.sid group by student_id HAVING count(student_id) > 1
 
 
八、查詢學過「葉平」老師所教的全部課的同窗的學號、姓名；
 
    同上，只不過將001和002變成 in (葉平老師的全部課)
 
九、查詢課程編號「002」的成績比課程編號「001」課程低的全部同窗的學號、姓名；
    同第1題
 
 
十、查詢有課程成績小於60分的同窗的學號、姓名；
         
    select sid,sname from student where sid in (
        select distinct student_id from score where num < 60
    )
 
十一、查詢沒有學全全部課的同窗的學號、姓名；
    思路：
        在分數表中根據學生進行分組，獲取每個學生選課數量
        若是數量 == 總課程數量，表示已經選擇了全部課程
 
        select student_id,sname
        from score left join student on score.student_id = student.sid
        group by student_id HAVING count(course_id) = (select count(1) from course)
 
 
十二、查詢至少有一門課與學號爲「001」的同窗所學相同的同窗的學號和姓名；
    思路：
        獲取 001 同窗選擇的全部課程
        獲取課程在其中的全部人以及全部課程
        根據學生篩選，獲取全部學生信息
        再與學生錶鏈接，獲取姓名
 
        select student_id,sname, count(course_id)
        from score left join student on score.student_id = student.sid
        where student_id != 1 and course_id in (select course_id from score where student_id = 1) group by student_id
 
1三、查詢至少學過學號爲「001」同窗全部課的其餘同窗學號和姓名；
        先找到和001的學過的全部人
        而後個數 ＝ 001全部學科     ＝＝》 其餘人可能選擇的更多
 
        select student_id,sname, count(course_id)
        from score left join student on score.student_id = student.sid
        where student_id != 1 and course_id in (select course_id from score where student_id = 1) group by student_id having count(course_id) ＝ (select count(course_id) from score where student_id = 1)
 
1四、查詢和「002」號的同窗學習的課程徹底相同的其餘同窗學號和姓名；
         
        個數相同
        002學過的也學過
 
        select student_id,sname from score left join student on score.student_id = student.sid where student_id in (
            select student_id from score  where student_id != 1 group by student_id HAVING count(course_id) = (select count(1) from score where student_id = 1)
        ) and course_id in (select course_id from score where student_id = 1) group by student_id HAVING count(course_id) = (select count(1) from score where student_id = 1)
 
 
1五、刪除學習「葉平」老師課的score表記錄；
 
    delete from score where course_id in (
        select cid from course left join teacher on course.teacher_id = teacher.tid where teacher.name = '葉平'
    )
 
1六、向SC表中插入一些記錄，這些記錄要求符合如下條件：①沒有上過編號「002」課程的同窗學號；②插入「002」號課程的平均成績；
    思路：
        因爲insert 支持 
                inset into tb1(xx,xx) select x1,x2 from tb2;
        全部，獲取全部沒上過002課的全部人，獲取002的平均成績
 
    insert into score(student_id, course_id, num) select sid,2,(select avg(num) from score where course_id = 2)
    from student where sid not in (
        select student_id from score where course_id = 2
    )
     
1七、按平均成績從低到高 顯示全部學生的「語文」、「數學」、「英語」三門的課程成績，按以下形式顯示： 學生ID,語文,數學,英語,有效課程數,有效平均分；
    select sc.student_id,
        (select num from score left join course on score.course_id = course.cid where course.cname = "生物" and score.student_id=sc.student_id) as sy,
        (select num from score left join course on score.course_id = course.cid where course.cname = "物理" and score.student_id=sc.student_id) as wl,
        (select num from score left join course on score.course_id = course.cid where course.cname = "體育" and score.student_id=sc.student_id) as ty,
        count(sc.course_id),
        avg(sc.num)
    from score as sc
    group by student_id desc        
 
1八、查詢各科成績最高和最低的分：以以下形式顯示：課程ID，最高分，最低分；
     
    select course_id, max(num) as max_num, min(num) as min_num from score group by course_id;
 
1九、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；
    思路：case when .. then
    select course_id, avg(num) as avgnum,sum(case when score.num > 60 then 1 else 0 END)/count(1)*100 as percent from score group by course_id order by avgnum asc,percent desc;
 
20、課程平均分從高到低顯示（現實任課老師）；
 
    select avg(if(isnull(score.num),0,score.num)),teacher.tname from course
    left join score on course.cid = score.course_id
    left join teacher on course.teacher_id = teacher.tid
 
    group by score.course_id
 
 
2一、查詢各科成績前三名的記錄:(不考慮成績並列狀況)
    select score.sid,score.course_id,score.num,T.first_num,T.second_num from score left join
    (
    select
        sid,
        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,
        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 3,1) as second_num
    from
        score as s1
    ) as T
    on score.sid =T.sid
    where score.num <= T.first_num and score.num >= T.second_num
 
2二、查詢每門課程被選修的學生數；
     
    select course_id, count(1) from score group by course_id;
 
2三、查詢出只選修了一門課程的所有學生的學號和姓名；
    select student.sid, student.sname, count(1) from score
 
    left join student on score.student_id  = student.sid
 
     group by course_id having count(1) = 1
 
 
2四、查詢男生、女生的人數；
    select * from
    (select count(1) as man from student where gender='男') as A ,
    (select count(1) as feman from student where gender='女') as B
 
2五、查詢姓「張」的學生名單；
    select sname from student where sname like '張%';
 
2六、查詢同名同姓學生名單，並統計同名人數；
 
    select sname,count(1) as count from student group by sname;
 
2七、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_id,avg(if(isnull(num), 0 ,num)) as avg from score group by course_id order by avg     asc,course_id desc;
 
2八、查詢平均成績大於85的全部學生的學號、姓名和平均成績；
 
    select student_id,sname, avg(if(isnull(num), 0 ,num)) from score left join student on score.student_id = student.sid group by student_id;
 
2九、查詢課程名稱爲「數學」，且分數低於60的學生姓名和分數；
 
    select student.sname,score.num from score
    left join course on score.course_id = course.cid
    left join student on score.student_id = student.sid
    where score.num < 60 and course.cname = '生物'
 
30、查詢課程編號爲003且課程成績在80分以上的學生的學號和姓名；
    select * from score where score.student_id = 3 and score.num > 80
 
3一、求選了課程的學生人數
 
    select count(distinct student_id) from score
 
    select count(c) from (
        select count(student_id) as c from score group by student_id) as A
 
3二、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；
     
    select sname,num 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='張磊老師') order by num desc limit 1;
 
3三、查詢各個課程及相應的選修人數；
    select course.cname,count(1) from score
    left join course on score.course_id = course.cid
    group by course_id;
 
 
3四、查詢不一樣課程但成績相同的學生的學號、課程號、學生成績；
    select DISTINCT s1.course_id,s2.course_id,s1.num,s2.num from score as s1, score as s2 where s1.num = s2.num and s1.course_id != s2.course_id;
 
3五、查詢每門課程成績最好的前兩名；
 
    select score.sid,score.course_id,score.num,T.first_num,T.second_num from score left join
    (
    select
        sid,
        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,
        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 1,1) as second_num
    from
        score as s1
    ) as T
    on score.sid =T.sid
    where score.num <= T.first_num and score.num >= T.second_num
 
3六、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(student_id) > 1
 
3七、查詢所有學生都選修的課程的課程號和課程名；
    select course_id,count(1) from score group by course_id having count(1) = (select count(1) from student);
 
3八、查詢沒學過「葉平」老師講授的任一門課程的學生姓名；
    select student_id,student.sname from score
    left join student on score.student_id = student.sid
    where score.course_id not in (
        select cid from course left join teacher on course.teacher_id = teacher.tid where tname = '張磊老師'
    )
    group by student_id
 
3九、查詢兩門以上不及格課程的同窗的學號及其平均成績；
 
    select student_id,count(1) from score where num < 60 group by student_id having count(1) > 2
 
40、檢索「004」課程分數小於60，按分數降序排列的同窗學號；
    select student_id from score where num< 60 and course_id = 4 order by num desc;
 
4一、刪除「002」同窗的「001」課程的成績；
    delete from score where course_id = 1 and student_id = 2