主鍵：表中經(jīng)常有一個(gè)列或多列的組合，其值能唯一地標(biāo)識(shí)表中的每一行。這樣的一列或多列稱為表的主鍵，通過它可強(qiáng)制表的實(shí)體完整性。當(dāng)創(chuàng)建或更改表時(shí)可通過定義 PRIMARY KEY 約束來創(chuàng)建主鍵。一個(gè)表只能有一個(gè) PRIMARY KEY 約束，而且 PRIMARY KEY 約束中的列不能接受空值。由于 PRIMARY KEY 約束確保唯一數(shù)據(jù)，所以經(jīng)常用來定義標(biāo)識(shí)列。

表數(shù)據(jù)新增格式：insert into 表格名（列名） values（值）

先導(dǎo)入student和score表，表為Excel，可以自己編寫。

例子：

mysql> insert into student(id,class,number,name) values(81,4,19,'stu81');

mysql> insert into student(id,class,number) values(82,4,20);

mysql> insert into student values(83,4,21,'stu83');

mysql> alter table student change id id int(2) auto_increment;

注釋：auto_increment以1為單位自增長(zhǎng)的意思；

mysql> insert into student(class,number,name) values(4,22,'stu84');

mysql> alter table score change id id int(4) auto_increment;

注釋：auto_increment自增長(zhǎng)的意思。+1。輸入該命令，表格會(huì)在新輸入自動(dòng)新增長(zhǎng)新的一行，id也會(huì)成自增。

mysql> insert into score(class,number,maths,chinese,english) values(4,19,80,78,98);

mysql> insert into score(class,number,maths,chinese,english) values(4,20,98,88,68);

mysql> insert into score(class,number,maths,chinese,english) values(4,21,91,83,78);

mysql> insert into score(class,number,maths,chinese,english) values(4,22,67,83,88);

查詢表數(shù)據(jù)格式：select * from <表名> where

注釋：語句以逗號(hào)做分隔，*通配符，select是展示的意思，where是條件；

例子：查詢學(xué)生信息表中所有信息：select * from student;

查詢成績(jī)表中，列id，class，chinese的信息：select id,class,chinese from score;

3）表數(shù)據(jù)排序操作：升序：order by 降序：升序語句末尾加 desc

例子：查詢成績(jī)表中，列id，chinese的信息并且以列chinese排序

select id,chinese from score order by chinese;（升序）

select id,chinese from score order by chinese desc;（降序）

4）表數(shù)據(jù)查詢操作：

(1)查詢1班與2班的成績(jī)信息：mysql> select * from score where class=1 or class=2;

(2)查詢語文為77并且數(shù)學(xué)為88的成績(jī)信息：

mysql> select * from score where chinese=77 and maths=88;

(3)查詢1，2，3班的成績(jī)信息：mysql> select * from score where class in (1,2,3);

查詢不為4班的成績(jī)信息: mysql> select * from score where class not in (4);

(4)查詢不為4班的成績(jī)信息: mysql> select * from score where class !=4;

注釋： !在數(shù)據(jù)庫里面為否定的意思:

(5) 查詢1班到3班的成績(jī)信息: mysql> select * from score where class between 1 and 3;

注釋： between：在```之間，中間的意思:

(6) 查詢不為3班與4班的成績(jī)信息：mysql> select * from score where class not in (3,4);

(7)查詢語文成績(jī)大于等于80小于等于90的成績(jī)信息

mysql>select * from score where chinese>=80 and chinese<=90;

(8) 統(tǒng)計(jì)成績(jī)表的總數(shù):mysql> select count(*) from score;

(9) 按照英語去重，顯示英語成績(jī)信息:mysql> select distinct English from score;

注釋： distinct 去除重復(fù)的意思；

(10) 顯示4到7行的數(shù)據(jù):mysql> select * from score limit 3,4;

注釋：數(shù)據(jù)庫數(shù)據(jù)排列：0，1，2，3； 3顯示第4行； 4，5，6，7共有4行； 3，4 ；

3表示第4行，4表示從第3行開始到第7行，共有4行；

(11) 按chinese排序，顯示4,5行數(shù)據(jù): mysql> select * from score order by chinese limit 3,2;

(12) 查詢出學(xué)生姓名為stu10的學(xué)生信息：mysql> select * from student where name='stu10';

注釋：只要不是數(shù)字，有漢字?jǐn)?shù)字字母多種組成的形式都要加單引號(hào)，表示字符串。

(13) 查詢出學(xué)生姓名為stu10或者stu15的學(xué)生信息:

mysql> select * from student where name in ('stu10','stu15');

(14) 分組查詢每個(gè)班的人數(shù)：mysql> select class,count(*) from student group by class;

作業(yè)：

1，查詢4班的成績(jī)信息：select * from score where class=4；

;

2，查詢4班，語文成績(jī)大于80小于90的成績(jī)信息：

select * from score where class in (4) and chinese>80 and chinese<90;

3，查詢學(xué)生表中5到10行的數(shù)據(jù)：select * from student limit 4,6;

4，顯示3班語文成績(jī)?yōu)?0，數(shù)學(xué)成績(jī)?yōu)?8，的class與number信息,：

select class, number from score where class=3 and chinese=90 and maths=68;

5，查詢出4班成績(jī)并且按語文成績(jī)倒序排序：

select * from score where class=4 order by chinese desc;

6，查詢2班與3班，語文成績(jī)與數(shù)學(xué)成績(jī)都大于80的class與number信息：

select class, number from score where class in (2,3) and chinese>80 and maths>88;

7，查詢學(xué)生名不為stu18，stu22，stu35，stu46，stu54，stu72班級(jí)與學(xué)號(hào)信息

分組與函數(shù)查詢

溫馨提示：分組之后查詢其他函數(shù)結(jié)果是不正確的；

分組函數(shù)：group by

按班級(jí)分組，查詢出每班數(shù)學(xué)最高分：select class,max(maths) from score group by class;

不分班級(jí)查詢總?cè)藬?shù)最高分: select max(maths) from score;

注釋: max:最大值;

按班級(jí)分組，查詢出每班數(shù)學(xué)最低分：select class,min(maths) from score group by class;

注釋:最小值min；

按班級(jí)分組，查詢出每班數(shù)學(xué)總分：select class,sum(maths) from score group by class;

注釋：sum：總分；

按班級(jí)分組，查詢出每班數(shù)學(xué)平均分：select class,avg(maths) from score group by class;

注釋：avg：平均值：

按班級(jí)分組，查詢出每班學(xué)生總數(shù)：select class,count(*) from score group by class;

注釋：count:有價(jià)值的；

語句執(zhí)行順序: from先執(zhí)行，后執(zhí)行where, 再接著執(zhí)行having,limit等。

例句：

select class,max(maths) from score where group by(分組) class having(所有) order by(排序) limit

from后面可以加茲查詢，語句先執(zhí)行后面再執(zhí)行前面

運(yùn)算符：數(shù)學(xué)運(yùn)算符

mysql> select class,number,maths,maths+5 from score;

mysql>select class,number,chinese+maths+english from score;

mysql> select *,maths+chinese+english as total from score;

mysql> select *,maths+chinese+english as total from score order by total desc;

mysql> select class*2,number,maths+chinese+english as total from score order by total desc;

連接查詢

左連接查詢：

mysql> select stu.*,sc.*,maths+sc.chinese+sc.english from student stu left join score sc on stu.id=sc.id;

注釋：stu:為別名。student stu left join score：student:為主表，score為副表顯示。 left join:為左連接。兩表關(guān)聯(lián)：其ID必須一一對(duì)應(yīng)（stu.id=sc.id）；

右連接查詢：

mysql> select stu.*,sc.*,maths+sc.chinese+sc.english from student stu right join score sc on stu.id=sc.id;

內(nèi)連接查詢：兩個(gè)表同時(shí)都有的內(nèi)容才會(huì)顯示。

mysql> select stu.*,sc.*,maths+sc.chinese+sc.english from student stu join score sc on stu.id=sc.id;

顯示查詢數(shù)據(jù)連接：把后表與前排合起來在一個(gè)表顯示。

select id,name,class from student union select class,number,maths from score;

多表查詢

select name,student.class,student.number,maths,chinese,english from student,score where student.id=score.id;

題目練習(xí)

顯示總分大于200的學(xué)生信息：

select stu.name,sc.maths,sc.chinese,sc.english,sc.maths+sc.chinese+sc.english from student stu,score sc where stu.id=sc.id and sc.maths+sc.english+sc.chinese>200;

顯示班級(jí)總數(shù)大于等于20的班級(jí)：

select class,count(*) as total from student group by class having total>=20;

顯示人總數(shù)大于等于20的班級(jí)的成績(jī)信息：

mysql> select sc.class,sc.number,sc.maths from score sc,(select class,count(*) as total from student group by class having total>=20) s where sc.class=s.class;

注釋：commit：保存提交的意思，一般文件刪除修改都要做保存；

Rollback：撤回的意思，命令執(zhí)行后；可以撤回為修改刪除前的數(shù)據(jù)；

truncate table score：永久刪除的意思，盡量少用，刪除則無記錄找回；

select now()：查詢現(xiàn)在的時(shí)間；

修改語句

update 表名 set where 條件

mysql> update student set birth=1988,department='中文系' where id=901 and name='張老大';

把張老大的出生日期修改為1988，院系修改成中文系

mysql> update student set birth=birth-5;

把所有學(xué)生的年紀(jì)增加5歲；

刪除語句

mysql> delete from student where id=901;

刪除901同學(xué)的，學(xué)生信息

mysql> delete from student where address like "湖南%";

刪除湖南籍學(xué)生的信息

mysql> delete from student;

清空學(xué)生表信息

字符查詢like

mysql> select * from student where address like '北京%';

查詢地址為北京的學(xué)生信息

mysql> select * from student where address like '%北京%平%';

查詢地址為北京市昌平區(qū)的學(xué)生信息

mysql> select * from score where stu_id in (select id from student where address like '湖南%');

查詢湖南籍學(xué)生的成績(jī)信息；

作業(yè)：

1，把張三的計(jì)算機(jī)成績(jī)修改成60分

update score set grade=60 where stu_id in(select id from student where name='張三')and c_name='計(jì)算機(jī)';

2，把計(jì)算機(jī)科目的分?jǐn)?shù)降低5分

update score set grade=grade-5 where c_name='計(jì)算機(jī)';

3，把湖南省學(xué)生計(jì)算機(jī)分?jǐn)?shù)提高5分

update score set grade=grade+5 where c_name='計(jì)算機(jī)'and stu_id in(select id from student where address like '湖南%');

4，把學(xué)號(hào)為904的學(xué)生，計(jì)算機(jī)成績(jī)改為85

update score set grade=85 where c_name='計(jì)算機(jī)' and stu_id=904;

5，刪除904學(xué)生的成績(jī)

delete from score where stu_id=904;

6，刪除湖南籍貫學(xué)生的成績(jī)

delete from score where stu_id in(select id from student where address like '湖南%');

7，刪除王姓與張姓同學(xué)英語成績(jī)

delete from score where stu_id in (select id from student where name like '王%'or name like '張%') and c_name='英語';

8，刪除年紀(jì)大于30的學(xué)生的計(jì)算機(jī)成績(jī)

delete from score where stu_id in (select id from student where 2016-birth>30);

MySQL練習(xí)

創(chuàng)建student和score表

CREATE TABLE student (id INT(10) NOT NULL PRIMARY KEY ,name VARCHAR(20) NOT NULL ,sex VARCHAR(4) ,birth YEAR,department VARCHAR(20) ,address VARCHAR(50) );

創(chuàng)建score表，SQL代碼如下：

CREATE TABLE score (id INT(10) NOT NULL PRIMARY KEY AUTO_INCREMENT ,

stu_id INT(10) NOT NULL ,c_name VARCHAR(20) ,grade INT(10));

為student表和score表增加記錄

向student表插入記錄的INSERT語句如下：

INSERT INTO student VALUES( 901,'張老大', '男',1984,'計(jì)算機(jī)系', '北京市海淀區(qū)');

INSERT INTO student VALUES( 902,'張老二', '男',1987,'中文系', '北京市昌平區(qū)');

INSERT INTO student VALUES( 903,'張三', '女',1991,'中文系', '湖南省永州市');

INSERT INTO student VALUES( 904,'李四', '男',1993,'英語系', '遼寧省阜新市');

INSERT INTO student VALUES( 905,'王五', '女',1990,'英語系', '福建省廈門市');

INSERT INTO student VALUES( 906,'王六', '男',1989,'計(jì)算機(jī)系', '湖南省衡陽市');

INSERT INTO student VALUES( 907,'老七', '男',1991,'計(jì)算機(jī)系', '廣東省深圳市');

INSERT INTO student VALUES( 908,'老八', '女',1990,'英語系', '山東省青島市');

向score表插入記錄的INSERT語句如下：

INSERT INTO score VALUES(NULL,901, '計(jì)算機(jī)',98);

INSERT INTO score VALUES(NULL,901, '英語', 80);

INSERT INTO score VALUES(NULL,902, '計(jì)算機(jī)',65);

INSERT INTO score VALUES(NULL,902, '中文',88);

INSERT INTO score VALUES(NULL,903, '中文',95);

INSERT INTO score VALUES(NULL,904, '計(jì)算機(jī)',70);

INSERT INTO score VALUES(NULL,904, '英語',92);

INSERT INTO score VALUES(NULL,905, '英語',94);

INSERT INTO score VALUES(NULL,906, '計(jì)算機(jī)',90);

INSERT INTO score VALUES(NULL,906, '英語',85);

INSERT INTO score VALUES(NULL,907, '計(jì)算機(jī)',98);

1.查詢student表的第2條到4條記錄

select * from student limit 1,3;

2.從student表查詢所有學(xué)生的學(xué)號(hào)（id）、姓名（name）和院系（department）的信息

mysql> select id,name,department from student;

3.從student表中查詢計(jì)算機(jī)系和英語系的學(xué)生的信息

select * from student where department in ('計(jì)算機(jī)系' ,'英語系');

4.從student表中查詢年齡23~26歲的學(xué)生信息

select * from student where birth between 1990 and 1993; 2016-23=1993 2016-26=1990

select id,name,sex,2016-birth as age,department,address from student where 2016-birth;

5.從student表中查詢每個(gè)院系有多少人

select department,count(id) from student group by department;

6.從score表中查詢每個(gè)科目的最高分。

select c_name,max(grade) from score group by c_name;

7.查詢李四的考試科目（c_name）和考試成績(jī)（grade）

select c_name,grade from score,student where score. stu_id=student.id and name='李四';

select c_name,grade from score where stu_id=(select id from student where name='李四'）;

8.用連接的方式查詢所有學(xué)生的信息和考試信息

select stu.*,sc.* from student stu left join score sc on stu.id=sc.id;

9.計(jì)算每個(gè)學(xué)生的總成績(jī)

select stu_id,sum(grade) from score group by stu_id;

10.計(jì)算每個(gè)考試科目的平均成績(jī)

select c_name,avg(grade) from score group by c_name;

11.查詢計(jì)算機(jī)成績(jī)低于95分的學(xué)生信息

select student.*, grade from score,student where student.id=score.stu_id and c_name like '計(jì)算機(jī)' and grade<95;

12.查詢同時(shí)參加計(jì)算機(jī)和英語考試的學(xué)生的信息

select student.*,c_name from student,score where student.id=score.stu_id and student.

id =any( select stu_id from score where stu_id in (select stu_id from score where c_name= '計(jì)算機(jī)') and c_name= '英語' );

select * from student where id in(select stu_id from score where stu_id in (select stu_id from

score where c_name='計(jì)算機(jī)' )and c_name='英語');

select student.* from student,(select stu_id from score where stu_id in (select stu_id from score where c_name='計(jì)算機(jī)' )and c_name='英語') t1 where student.id=t1.stu_id;

select * from student where id in (select stu_id from score sc where sc.c_name='計(jì)算機(jī)') and id in (select stu_id from score sc where sc.c_name='英語');

13.將計(jì)算機(jī)考試成績(jī)按從高到低進(jìn)行排序

select c_name,grade from score where c_name='計(jì)算機(jī)' order by grade;

14.從student表和score表中查詢出學(xué)生的學(xué)號(hào)，然后合并查詢結(jié)果

select id from student union select id from score;

15.查詢姓張或者姓王的同學(xué)的姓名、院系和考試科目及成績(jī)

select name,department,c_name,grade from score sc,student st where st.id=sc.stu_id and (name like'張%'or name like '王%');

16.查詢都是湖南的學(xué)生的姓名、年齡、院系和考試科目及成績(jī)中文系

select name,2016-birth age,department,address,c_name,grade from student,score where student.id=score.stu_id and address like'湖南%';

17.查詢每個(gè)科目的最高分的學(xué)生信息.

分解： score=t1, t2=select c_name,max(grade) as grade from score group by c_name， t1.stu_id注解

分解： select * from student where id in (select t1.stu_id from score t1,t2 t2 where t1.c_name=t2.c_name and t1.grade=t2.grade);

select * from student where id in (select t1.stu_id from score t1,(select c_name,max(grade) as grade from score group by c_name) t2 where t1.c_name=t2.c_name and t1.grade=t2.grade);

select student.* from student,(select score.* from score,(select max(grade) grade,c_name from score group by c_name) t1 where score.c_name=t1.c_name and score.grade=t1.grade) t2 where student.id=t2.stu_id;

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