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SQL增删查改

 

--  sql 结构化查询语言  操作数据库的


-- 注释  --空格


-- 创建数据库

create database itquanmingxing;


-- 创建数据库的时候设置编码

create database itquanmingxing2  CHARACTER set utf8;


-- 删除数据库  

drop database itquanmingxing;


-- 删除数据库前 先判断数据库是否存在

drop database if exists  itquanmingxing;


-- 使用库

use itquanmingxing2;


-- 创建表

create table teacher

(

   tid int primary key ,

   tname varchar(2),

   professional_title varchar(20)

);


-- 打印表结构

desc teacher;


-- 查询表数据  

select * from teacher;


-- 删除表

drop table teacher;


drop table if exists teacher;


create table teacher

(

   tid int primary key  auto_increment, -- 自增 默认从1开始 每次自增1

   tname varchar(2),

   professional_title varchar(20)

)ENGINE=INNODB default charset=utf8 auto_increment=100; -- 自增 从100开始


select * from teacher;


-- 修改表


-- 添加列

alter table teacher    -- 修改 表  表名  

add salary float    -- 添加  列名  列的属性


-- 删除列

alter table teacher

drop column salary      -- 删除  列  列名


-- 修改列

alter table teacher

modify column tname varchar(20)  -- 修改 列  列名  列的属性


desc teacher;


-- 给表添加约束

create table student

(

  sid int primary key auto_increment,  -- 主键约束

  sname varchar(20) not null,  -- 非空约束

  sex char(2) default  '男',  -- 默认约束

  card_id char(18) unique,  -- 唯一约束

  age int, -- check(age>=18 and age<=28)

  tid int,  


  foreign key(tid) REFERENCES teacher(tid)     -- 外键约束  必须是其它表中的主键

)ENGINE=INNODB;


select * from teacher;


select * from student;


-- 实体完整性: 主键约束 唯一约束

-- 域完整性 : not null  default  

-- 引用完整性: 外键


-- insert 添加数据


select * from teacher;


-- 添加表中的所有列

insert into teacher values(null,'daimenglaoshi','高级');


-- 添加部分列

insert into teacher(tname) values('wanglaoshi');


insert into teacher values(null,'zhanglaoshi','高级');


insert into student values(null,'lisi',default,556777,null,101);


insert into student values(null,'wangwu',default,888888,null,102);


insert into student values

(null,'zhaoliu',default,99999,null,101),

(null,'王二',default,77777,null,102);



-- update  更新

-- 语法: update  表名 set 新的值 where 条件


-- 将王五的性别改为女

update student set sex='女' where sname='wangwu'



-- 将zhaoliu的性别改为女 将年龄改为18

update student set sex='女',age=18 where sname='zhaoliu'  


-- 将所有年龄为null的学生的年龄改为28

update student set age=28 where age is null;


select * from student;


-- 将所有的年龄都清空

update student set age = null;


-- 将学号在2--5范围内的学生的年龄改为18

update student set age=18 where sid>=2 and sid<=5



-- delete  删除


-- delete from 表名  where 条件


-- 删除表中所有的数据

delete from student;


delete from student where  sid=7



delete from student where age is null


delete from student where age>28 or tid=102


-- insert  update  delete  dml语言:数据操纵语言  

-- 操纵的是数据 跟结构无关 不会影响到结构的


-- 查询

-- select  

-- 简单查询


use itquanmingxing2;


-- 1.查询所有列(查询整张表的数据)

-- * 所有的列

select * from student;


-- 2.查询部分列

select sname,age from student;


-- 3.查询的时候 给字段取别名

select sname as '姓名',age as '年龄' from student;

-- as可以省略

select sname  '姓名',age  '年龄' from student;


--  


update student set age=19 where sid=2;

update student set age=29 where sid=5;

update student set age=27 where sid=6;


-- 4.查询的时候排序

select * from student order by age -- asc 默认是升序


select * from student order by age desc -- 降序


-- 排序可以针对多个字段

select * from student order by tid ,age desc  


-- 5. 读取部分记录  limit 偏移量 ,记录数

-- 查询年龄最大的前三个学生

select * from student order by age desc limit 0,3


select * from student order by age desc limit 1,3


-- 分页查询

select * from student limit 0,2


select * from student limit 2,2


-- 6. 去掉重复行

select distinct tid from student  


-- 7. 带条件的查询


-- 1) 关系运算符 > < >= <= = !=

select * from student where sex='男'



-- 2) and  or  

select * from student where sex='男' and age>18;  

select * from student where sex='男' && age>18;  


-- 查询 tid=101号老师的学生 或者年龄>25

select * from student where tid=101 or age>25

select * from student where tid=101 || age>25


select * from student where age>=18 and age<=28

-- 3) between and   在18到28之间

select * from student where age between 18 and 28


--  4) in  not in  在 某个范围内的  

select * from student where sid in (2,3,6);

-- 等价于

select * from student where sid=2 or sid=3 or sid=6


select * from student where sid not in (2,3,6);



update student set tid=null where sid=2


select * from student  


-- 5) is null  is not null查询出tid为null的学生

select * from student where tid is null


select * from student where tid is not null


-- 6) like  not like  查询 模糊查找


insert into student values(null,'张三',default,8767,null,101);


insert into student values(null,'张四',default,8989,null,102);


insert into student values(null,'小张三',default,89898,null,102);


select * from student


--  查询姓张的所有学生

-- % 通配符  匹配任意字符任意多个 包括0个

select * from student where sname like '张%'

-- 查询名字中带张的

select * from student where sname like '%张%'


-- 查询两个字的名字 第二个字为三的

-- _通配符 匹配一个任意字符  

select * from student where sname like '_三'


select * from student where sname not  like '_三'


-- 查询第二个字为张的

select * from student where sname like '_张%'


-- 查询最后一个字是三或者四的

select * from student where sname like '%三' or sname like  '%四'



-- 聚合查询(集函数)


-- 1) count() 返回总记录数

select count(*) from student


-- 查询当前字段的总个数 (null 不计算)

select count(tid) from student


-- 2) max() 最大值

select max(age) from student


-- 3) min()最小值

select min(age) from student


-- 4) sum() 求和

select sum(age) from student


-- 5) avg() 求平均值

select avg(age) from student


-- 请帮我查询年龄最大的学生的信息


-- 普通字段不能和聚合函数放在一起查询  除非 聚合函数和 group by 的字段放一起

-- 或者聚合函数放在子查询中

--  select sname,max(age) from student  -- 错误的

select sname,age from student where age=

(select max(age) from student)



-- 查询男生和女生中年龄最大的学生

update student set age=23,sex='女' where sid=7


select sex,max(age) from student group by sex


select * from student


-- 对分组后的结果进行删选  用having  

select tid,count(*) from student group by tid  having  count(*)>2


-- 高级查询  多表联查

use itquanmingxing2;


select * from student;


select * from teacher;


-- 联接查询

-- 查询所有选择了教师的学生信息以及对应的老师信息

--  

-- 1)内联接  两张表都有的记录才查询出来  

-- 简化写法

select * from student,teacher  where  student.tid=teacher.tid

-- 标准写法

select * from student inner join teacher on student.tid=teacher.tid



-- 联接成一张表后  可以在此基础上做查询  

select sname,tname from student inner join teacher on student.tid=teacher.tid

where sid=8  


-- 也可以直接用and

select sname,tname from student inner join teacher on student.tid=teacher.tid

and sid=8  


-- 查询所有的学生信息以及对应的老师信息

-- 2) 左外联接   左边这张表的数据全部查询出来 右边只显示与之能关联的数据

select * from student left outer  join teacher  

on student.tid=teacher.tid


select * from teacher


-- 3)右外  右边的表为主表  

select * from student right outer  join teacher  

on student.tid=teacher.tid


select * from teacher left outer  join  student

on student.tid=teacher.tid  



select * from teacher left outer  join  student

on student.tid=teacher.tid  where teacher.tid=101 and sex='男'


-- 嵌套子查询


-- 查询 lisi的教师名称


select tname from teacher where tid=

(select tid from student where sname='lisi')


-- 也可以用联接查询

select tname from student inner join teacher on student.tid=teacher.tid  

and sname='lisi'



select tname from teacher where tid in

(select distinct tid from student where sex='男')



-- all any  


-- 查询年龄>所有的女生的男生信息


select * from student where age>all

(select age from student where sex='女') and sex='男'

-- >all等价于 >max()  

select * from student where age>

(select max(age) from student where sex='女') and sex='男'


-- 查询年龄>任意一个女生的男生信息

select * from student where age > any

(select age from student where sex='女') and sex='男'


select * from student where age >  

(select min(age) from student where sex='女') and sex='男'




select * from student;

select * from teacher;


use itquanmingxing2;


select sname '姓名' from student


select * from student a inner join teacher b on a.tid=b.tid


update student set age=18 where sid=7


select * from  

(select * from student where sex='男') a,


(select * from student where sex='女') b where a.age=b.age






















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