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  • 数据库的增删改查

    1、数据库:person

    创建 create databases person;

    查看 show databases;

    指定使用  use person;

    删除 drop databases person;

    2、表:person

    creat table person(

    列名1 数据类型描述,

    列名2 数据类型描述,

    列名3 数据类型描述,

    列名4 数据类型描述,

    );

    creat table person(

    id int unsigned not null auto_increment primary key,

    name char(10) not null,

    age tinyint not null,

    sex varchar(5) not null,

    tel char(13) null default "-"

    );

    [unsigned 无符号, not null 非空, auto_increment 递增, primary key 主键]

    显示表:show tables;

    查看表结构:

    describe person ;

    或者  show columns from/ in person;

    根据旧表创建新表

    create table student like person;

    create table student as select id,name from person;

    复制整个表

    create table student as select * from person;

    [as 可以省略]

    删除表:

    drop table person;

    重新命名表:

    rename table person to person1

    或者

    alter table person rename person1

    表名:person 

    字段:id,name,age

    1 张三 20

    2 李四 22

    3 王五 23

    查询:

    select id,name,age from person;

    select * from person

    select id from person where name="李四"

    selext id from person where name like "%王%"  名字中带有王字的id

    select name from person where age is null

    select name from person where id>=2 order by desc    降序

    select name from person where id>=2                  默认升序

    select name from person where id>=2 order by asc    升序

    select top 2 name from person              mysql显示name的前二行

    select * from person  where rownum < 2    oracle 显示name的前二行

    select name '成都' as 地址 from person    查询name列 添加地址列 值为成都

    select name as 姓名 from person where id=2 选出表中id为2的行,显示name列,并将name列改为姓名显示

    删除:delete from person where id=1;

    修改:update person set name="刘德华" where id=2;

    增加:insert into person(id,name,age) values(4,'刘能',24);

          或者不要列名,按表定义的顺序填写

          insert into person values(4,'刘能',24);

    另外一张表:

    student

    insert into student(id,name,age) select id,name,age from person

    删除整个表的数据

    truncate table person

    添加列:

    表的最后添加

    alter table  person add  sex char(3) not null; 

    在指定的列后面添加:

    alter table person add address cha(5) after age;

    在表的最前面添加

    alter table person add address cha(5) first;

    修改列的列名:

    alter table person change address address1 char(10) null default "-";

    修改列的数字类型:

    alter table person change name name char(20) not null;

    删除列:

    删除表person 中sex列;

    alter table person drop sex;

    求某列数据总数(不包含缺省)

    select count(age) as totalcount from person;

    统计表的总行数:

    select conut(*) as totalcount from person;

    求某列数据的总和;

    select sum(id) as idsum from person;

    求某列数据的平均值;

    select avg(age) as ageavg from person;

    求某列数据的最大最小值:

    slect max(age) as maxage from person;

    slect min(age) as minage from person;

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  • 原文地址:https://www.cnblogs.com/classics/p/9747171.html
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