目录

数据库常用命令

数据库的创建

数据表的操作

表数据的增删查改

分组与函数查询

运算符:数学运算符

连接查询

多表查询

修改语句

删除语句

字符查询like

MySQL练习

总结感谢每一个认真阅读我文章的人!!!

重点:配套学习资料和视频教学


数据库常用命令

进入数据库,在win系统下,打开cmd,切换用户权限,进入root。

沒權限,用root登錄:mysql-uroot
如果root有密碼:mysql-uroot-p

数据库的创建

查询所有数据库:show databases;

创建数据库:create database ;

删除数据库:drop database ;

进入数据库:use ;

数据表的操作

1)查询数据库下表:show tables;

2)创建表:create table student(id int(4) primary key,name char(20));

注释: id为表的第一列;

int数字类型;

primary key主键的意思,列不能重复。

Name为表的第二列名字。

char:类型;

创建表:create table score(id int(4) not null,class int(2));

注释: not null字段不能为空。

创建表:create table student1(id int(4) not null,name char(20));

Field (列名),Type(字段类型),null(是否为空),key(主键)

3)查看表结构:describe student; desc student;

4)修改表名:alter table rename ;

5)删除表:drop table ;

6)修改表字段信息:alter table student change id id int(20);

7)增加表字段信息:alter table student1 add class int(4) not null after id;

8)删除一个表字段:alter table student1 drop number;

表数据的增删查改

提示:在数据库导入表时,要修改列的字段类型并设置主键;

主键:表中经常有一个列或多列的组合,其值能唯一地标识表中的每一行。这样的一列或多列称为表的主键,通过它可强制表的实体完整性。当创建或更改表时可通过定义 PRIMARY KEY 约束来创建主键。一个表只能有一个 PRIMARY KEY 约束,而且 PRIMARY KEY 约束中的列不能接受空值。由于 PRIMARY KEY 约束确保唯一数据,所以经常用来定义标识列

  1. 表数据新增格式:insert into 表格名(列名) values(值)

先导入student和score表,表为Excel,可以自己编写。

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;

注释:auto_increment以1为单位自增长的意思;

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

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

注释:auto_increment自增长的意思。+1。输入该命令,表格会在新输入自动新增长新的一行,id也会成自增。

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);

  1. 查询表数据格式:select * from where

注释:语句以逗号做分隔,*通配符,select是展示的意思,where是条件;

例子: 查询学生信息表中所有信息:select * from student;

查询成绩表中,列id,class,chinese的信息:select id,class,chinese from score;

3)表数据排序操作:升序:order by 降序:升序语句末尾加 desc

例子:查询成绩表中,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)表数据查询操作:

(1)查询1班与2班的成绩信息:mysql>select * from score where class=1 or class=2;

(2)查询语文为77并且数学为88的成绩信息:

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

(3)查询1,2,3班的成绩信息:mysql>select * from score where class in (1,2,3);

查询不为4班的成绩信息: mysql>select * from score where class not in (4);

(4)查询不为4班的成绩信息: mysql> select * from score where class !=4;

注释: !在数据库里面为否定的意思:

(5) 查询1班到3班的成绩信息: mysql>select * from score where class between 1 and 3;

注释: between:在“`之间,中间的意思:

(6) 查询不为3班与4班的成绩信息:mysql> select * from score where class not in (3,4);

(7)查询语文成绩大于等于80小于等于90的成绩信息

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

(8) 统计成绩表的总数:mysql>select count(*) from score;

(9) 按照英语去重,显示英语成绩信息:mysql> select distinct English from score;

注释: distinct 去除重复的意思;

(10) 显示4到7行的数据:mysql> select * from score limit 3,4;

注释:数据库数据排列:0,1,2,3; 3显示第4行; 4,5,6,7共有4行; 3,4 ;

3表示第4行,4表示从第3行开始到第7行,共有4行;

(11) 按chinese排序,显示4,5行数据: mysql>select * from score order by chinese limit 3,2;

(12) 查询出学生姓名为stu10的学生信息:mysql> select * from student where name=’stu10′;

注释:只要不是数字,有汉字数字字母多种组成的形式都要加单引号,表示字符串。

(13) 查询出学生姓名为stu10或者stu15的学生信息:

mysql>select * from student where name in (‘stu10′,’stu15’);

(14) 分组查询每个班的人数:mysql>select class,count(*) from student group by class;

作业:

1,查询4班的成绩信息:select * from score where class=4;

;

2,查询4班,语文成绩大于80小于90的成绩信息:

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

3,查询学生表中5到10行的数据:select * from student limit 4,6;

4,显示3班语文成绩为90,数学成绩为68,的class与number信息,:

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

5,查询出4班成绩并且按语文成绩倒序排序:

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

>

6,查询2班与3班,语文成绩与数学成绩都大于80的class与number信息:

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

7,查询学生名不为stu18,stu22,stu35,stu46,stu54,stu72班级与学号信息

分组与函数查询

温馨提示:分组之后查询其他函数结果是不正确的;

分组函数:group by

按班级分组,查询出每班数学最高分:select class,max(maths) from score group by class;

不分班级查询总人数最高分: select max(maths) from score;

注释: max:最大值;

按班级分组,查询出每班数学最低分:select class,min(maths) from score group by class;

注释:最小值min;

按班级分组,查询出每班数学总分:select class,sum(maths) from score group by class;

注释:sum:总分;

按班级分组,查询出每班数学平均分:select class,avg(maths) from score group by class;

注释:avg:平均值:

按班级分组,查询出每班学生总数:select class,count(*) from score group by class;

注释:count:有价值的;

语句执行顺序: from先执行,后执行where, 再接着执行having,limit等。

例句:

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

from后面可以加兹查询,语句先执行后面再执行前面

运算符:数学运算符

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;

连接查询

左连接查询:

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

注释:stu:为别名。student stu left join score:student:为主表,score为副表显示。 left join:为左连接。 两表关联:其ID必须一一对应(stu.id=sc.id);

右连接查询:

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

内连接查询:两个表同时都有的内容才会显示。

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

显示查询数据连接:把后表与前排合起来在一个表显示。

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

多表查询

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

题目练习

显示总分大于200的学生信息:

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;

显示班级总数大于等于20的班级:

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

显示人总数大于等于20的班级的成绩信息:

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;

注释:commit:保存提交的意思,一般文件删除修改都要做保存;

Rollback:撤回的意思,命令执行后;可以撤回为修改删除前的数据;

truncate table score:永久删除的意思,尽量少用,删除则无记录找回;

select now():查询现在的时间;

修改语句

update 表名 set where 条件

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

把张老大的出生日期修改为1988,院系修改成中文系

mysql> update student set birth=birth-5;

把所有学生的年纪增加5岁;

删除语句

mysql> delete from student where id=901;

删除901同学的,学生信息

mysql> delete from student where address like “湖南%”;

删除湖南籍学生的信息

mysql> delete from student;

清空学生表信息

字符查询like

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

查询地址为北京的学生信息

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

查询地址为北京市昌平区的学生信息

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

查询湖南籍学生的成绩信息;

作业:

1,把张三的计算机成绩修改成60分

update score set grade=60 where stu_id in(select id from student where name=’张三’)and c_name=’计算机’;

2,把计算机科目的分数降低5分

update score set grade=grade-5 where c_name=’计算机’;

3,把湖南省学生计算机分数提高5分

update score set grade=grade+5 where c_name=’计算机’and stu_id in(select id from student where address like ‘湖南%’);

4,把学号为904的学生,计算机成绩改为85

update score set grade=85 where c_name=’计算机’ and stu_id=904;

5,删除904学生的成绩

delete from score where stu_id=904;

6,删除湖南籍贯学生的成绩

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

7,删除王姓与张姓同学英语成绩

delete from score where stu_id in (select id from student where name like ‘王%’or name like ‘张%’) and c_name=’英语’;

8,删除年纪大于30的学生的计算机成绩

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

MySQL练习

创建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) );

创建score表,SQL代码如下:

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));

为student表和score表增加记录

向student表插入记录的INSERT语句如下:

INSERT INTO student VALUES( 901,’张老大’, ‘男’,1984,’计算机系’, ‘北京市海淀区’);

INSERT INTO student VALUES( 902,’张老二’, ‘男’,1987,’中文系’, ‘北京市昌平区’);

INSERT INTO student VALUES( 903,’张三’, ‘女’,1991,’中文系’, ‘湖南省永州市’);

INSERT INTO student VALUES( 904,’李四’, ‘男’,1993,’英语系’, ‘辽宁省阜新市’);

INSERT INTO student VALUES( 905,’王五’, ‘女’,1990,’英语系’, ‘福建省厦门市’);

INSERT INTO student VALUES( 906,’王六’, ‘男’,1989,’计算机系’, ‘湖南省衡阳市’);

INSERT INTO student VALUES( 907,’老七’, ‘男’,1991,’计算机系’, ‘广东省深圳市’);

INSERT INTO student VALUES( 908,’老八’, ‘女’,1990,’英语系’, ‘山东省青岛市’);

向score表插入记录的INSERT语句如下:

INSERT INTO score VALUES(NULL,901, ‘计算机’,98);

INSERT INTO score VALUES(NULL,901, ‘英语’, 80);

INSERT INTO score VALUES(NULL,902, ‘计算机’,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, ‘计算机’,70);

INSERT INTO score VALUES(NULL,904, ‘英语’,92);

INSERT INTO score VALUES(NULL,905, ‘英语’,94);

INSERT INTO score VALUES(NULL,906, ‘计算机’,90);

INSERT INTO score VALUES(NULL,906, ‘英语’,85);

INSERT INTO score VALUES(NULL,907, ‘计算机’,98);

1.查询student表的第2条到4条记录

select * from student limit 1,3;

2.从student表查询所有学生的学号(id)、姓名(name)和院系(department)的信息

mysql> select id,name,department from student;

3.从student表中查询计算机系和英语系的学生的信息

select * from student where department in (‘计算机系’ ,’英语系’);

4.从student表中查询年龄23~26岁的学生信息

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.从student表中查询每个院系有多少人

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

6.从score表中查询每个科目的最高分。

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

7.查询李四的考试科目(c_name)和考试成绩(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.用连接的方式查询所有学生的信息和考试信息

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

9.计算每个学生的总成绩

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

10.计算每个考试科目的平均成绩

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

11.查询计算机成绩低于95分的学生信息

select student.*, grade from score,student where student.id=score.stu_id and c_name like ‘计算机’ and grade<95;

12.查询同时参加计算机和英语考试的学生的信息

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= ‘计算机’) and c_name= ‘英语’ );

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

score where c_name=’计算机’ )and c_name=’英语’);

select student.* from student,(select stu_id from score where stu_id in (select stu_id from score where c_name=’计算机’ )and c_name=’英语’) t1 where student.id=t1.stu_id;

select * from student where id in (select stu_id from score sc where sc.c_name=’计算机’) and id in (select stu_id from score sc where sc.c_name=’英语’);

13.将计算机考试成绩按从高到低进行排序

select c_name,grade from score where c_name=’计算机’ order by grade;

14.从student表和score表中查询出学生的学号,然后合并查询结果

select id from student union select id from score;

15.查询姓张或者姓王的同学的姓名、院系和考试科目及成绩

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

16.查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩中文系

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.查询每个科目的最高分的学生信息.

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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