mysql 表操作

基础操作：

创建表；
    CREATE TABLE table_name(
        field1 type[完整约束性条件]，
        field2 type[完整约束性条件]，
        ........
        ........
        fieldn type  ##field字段名，type字段类型是必须的，字段不能重复
        )[CHARSET XXX]#指定字符编码，不写默认latin1
        
        创建一个员工表employee:
        
        CREATE TABLE employee(
            id int primary key auto_increment,
            name varchar(20),
            gender bit defaultn 1, --BIT类型表示0和1或者说false和true
            birthday date,
            entry_date date,
            job varchar(20),
            salary double(4,2) unsigned,
            resume text --最后一个字段不能叫逗号
            );
        
        /* 约束
            primary key (非空且唯一) : 能够唯一区分当前记录的字段成为主键
            unique 唯一
            not null 不为空
            auto_increment 主键字段必须为数字类型
            foreign key 外键约束  */  
        
        --查看表信息
        --desc table_name  查看表结构
        --show columns from table_name 查看表结构
        -- show create table tab_name 查看当前数据库表健 表语句
        
        
        --3 修改表结构
        --(1) 增加列（字段） 
        alter table tab_name add [column]列名 类型[完整约束性条件][first|after 字段名]；
        alter table user add addr varchar(20) not null unique first/after username;
        
        alter table employee
            add addr varchar(20),
            add age int first,#插到第一的位置
            add birth varchar(20) after name ;#插到name 后面
        
        --修改列 类型
        alter table tab_name modify 列名 类型 [完整约束类型][first|after]；
        alter table employee modify age tinyint default 20;
        alter table employee modify age int after id ;
        
        --修改列名
        alter table table_name change[cloumn] 列名 新列名 类型 [完整约束性条件][first|after 字段名];
        
        alter table employee change age Age int default 28 first;
        
        --删除一列
        alter table tab_name drop [column]列名；
        
        --修改表名
        rename table 表名 to  新表名；
        --修改表所用的字符集
        alter table tab_name charset 编码；
        --删除表
        drop table tab_name
        --添加主键 ，删除主键(主键： 非空且唯一 not null unique 唯一)
        
        alter table tab_name add primary key(字段名称)
        alter table user drop primary key;
        
        eg:
        create table test2(num int primary key auto_increment);
        alter table test modify id int;#删除了 auto_increment，但是主键任然在
        alter table test drop primary key;#加上这句才能删除主键
            
            
    -- 唯一索引
        alter table tab_name add unique [index|key] [索引名称](字段名称,...) 

        alter table users add unique(name)-- 索引值默认为字段名show create table users;
        alter table users add unique key user_name(name);-- 索引值为user_name

        -- 添加联合索引
        alter table users add unique index name_age(name,age);#show create table users;

        -- 删除唯一索引
        alter table tab_name drop {index|key} index_name

示例：

#创建数据库，指定字符集utf8

mysql> create database nulige character set utf8;
Query OK, 1 row affected (0.00 sec)mysql> show databases;+--------------------+| Database |+--------------------+

| information_schema |
| mysql              |
| nulige             |
| performance_schema |
| s3                 |
| s4                 |
| test               |
+--------------------+
7 rows in set (0.00 sec)

#进入nulige库
mysql> use nulige
Database changed

#查看表
mysql> show tables;
Empty set (0.00 sec)

#创建employee表
CREATE TABLE employee(

       id TINYINT PRIMARY KEY auto_increment,
       name VARCHAR(25),
       gender boolean,
       age  INT DEFAULT 19,
       department VARCHAR(20),
       salary DOUBLE(7,2)
);

#查看表
mysql> show tables;
+------------------+
| Tables_in_nulige |
+------------------+
| employee         |
+------------------+
1 row in set (0.00 sec)

#查看表结构
mysql> desc employee;
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| id         | tinyint(4)  | NO   | PRI | NULL    | auto_increment |
| name       | varchar(25) | YES  |     | NULL    |                |
| gender     | tinyint(1)  | YES  |     | NULL    |                |
| age        | int(11)     | YES  |     | 19      |                |
| department | varchar(20) | YES  |     | NULL    |                |
| salary     | double(7,2) | YES  |     | NULL    |                |
+------------+-------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

#增加一个字段
mysql> alter table employee add is_married tinyint(1);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0


#在表中增加1个字段
mysql> alter table employee add entry_date date not null;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

#增加二个字段
mysql> alter table employee add a INT,
    -> ADD B VARCHAR(20);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

#创建表
  mysql> create table A(id int);
  Query OK, 0 rows affected (0.01 sec)

 

  #查看表

  mysql> show tables;
  +------------------+
  | Tables_in_nulige |
  +------------------+
  | A |
  | emp |
  +------------------+
  2 rows in set (0.00 sec)

 

  #删除表

mysql> alter table employee DROP A;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0


#删除employee表中b字段
mysql> alter table employee DROP b,
    -> DROP entry_date;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0


#修改表中age字段的 null default 属于，并且在ID后面(after)
mysql> alter table employee modify age smallint not null default 18 after id;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

#查看表结构
mysql> desc employee;
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| id         | tinyint(4)  | NO   | PRI | NULL    | auto_increment |
| age        | smallint(6) | NO   |     | 18      |                |
| name       | varchar(25) | YES  |     | NULL    |                |
| gender     | tinyint(1)  | YES  |     | NULL    |                |
| department | varchar(20) | YES  |     | NULL    |                |
| salary     | double(7,2) | YES  |     | NULL    |                |
| is_married | tinyint(1)  | YES  |     | NULL    |                |
+------------+-------------+------+-----+---------+----------------+
7 rows in set (0.01 sec)

#修表employee表中字段名称：把department改成depart字段，并且把位置调到salary后面
mysql> alter table employee change department depart varchar(20) after salary;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

#查看表结构

mysql> desc employee;
  +------------+-------------+------+-----+---------+----------------+
  | Field | Type | Null | Key | Default | Extra |
  +------------+-------------+------+-----+---------+----------------+
  | id | tinyint(4) | NO | PRI | NULL | auto_increment |
  | age | smallint(6) | NO | | 18 | |
  | name | varchar(25) | YES | | NULL | |
  | gender | tinyint(1) | YES | | NULL | |
  | salary | double(7,2) | YES | | NULL | |
  | depart | varchar(20) | YES | | NULL | |
  | is_married | tinyint(1) | YES | | NULL | |
  +------------+-------------+------+-----+---------+----------------+
  7 rows in set (0.00 sec)

#修改表名
mysql> rename table employee to emp;
Query OK, 0 rows affected (0.00 sec)

#查看表
mysql> show tables;
+------------------+
| Tables_in_nulige |
+------------------+
| emp              |
+------------------+
1 row in set (0.00 sec)


#创建表
mysql> create table A(id int);
Query OK, 0 rows affected (0.01 sec)

#查看表
mysql> show tables;
+------------------+
| Tables_in_nulige |
+------------------+
| A                |
| emp              |
+------------------+
2 rows in set (0.00 sec)

#删除A表
mysql> drop table A;
Query OK, 0 rows affected (0.01 sec)

#查看表
mysql> show tables;
+------------------+
| Tables_in_nulige |
+------------------+
| emp              |
+------------------+
1 row in set (0.00 sec)