数据库的增删改查

针对库的增删改查

• 切换数据库

  语法： use 数据库名
  

• 增

  语法： create database 数据库名;
  
  mysql> create database db1;
  Query OK, 1 row affected (0.02 sec)
  

• 删

  语法： drop database 库名;
  

• 改

  最好不要修改数据库名
  

• 查

  查询所有的数据库；
  语法： show databases;
  查看当前所在库；
  语法： select database();
  

针对表的增删改查

• 增

  语法：
  	create table 表1(字段1 类型)， (字段2 类型);
  	
  	mysql> create table t1(id int, name varchar(16));
  	Query OK, 0 rows affected (0.09 sec)
  

• 删

  语法：
  	drop table 表1;
  

• 改

  语法：
  	1.修改表名：alter table 表1 rename 表2;
  	2.增加字段
  		alter table 表1 add 字段1 数据类型;
  	3.修改字段类型
  		alter table 表1 modify 字段1 类型；
  	4. 删除字段
  		alter table 表1 drop 字段名;
  	5. 修改字段
  		alter table 表1 change 旧字段名 新字段名 旧数据类型
  		alter table 表1 change 旧字段名 新字段名 新数据类型
  		
  
  mysql> alter table t1 rename t2;
  Query OK, 0 rows affected (0.04 sec)
  
  mysql> show tables;
  +---------------+
  | Tables_in_db1 |
  +---------------+
  | t2            |
  +---------------+
  1 row in set (0.00 sec)
  
  mysql> alter table t2 add age int;
  Query OK, 0 rows affected (0.03 sec)
  Records: 0  Duplicates: 0  Warnings: 0
  
  mysql> desc t2;
  +-------+-------------+------+-----+---------+-------+
  | Field | Type        | Null | Key | Default | Extra |
  +-------+-------------+------+-----+---------+-------+
  | id    | int         | YES  |     | NULL    |       |
  | name  | varchar(16) | YES  |     | NULL    |       |
  | age   | int         | YES  |     | NULL    |       |
  +-------+-------------+------+-----+---------+-------+
  3 rows in set (0.00 sec)
  
  mysql> alter table t2 modify name varchar(16);
  Query OK, 0 rows affected (0.01 sec)
  Records: 0  Duplicates: 0  Warnings: 0
  
  mysql> desc t2;
  +-------+-------------+------+-----+---------+-------+
  | Field | Type        | Null | Key | Default | Extra |
  +-------+-------------+------+-----+---------+-------+
  | id    | int         | YES  |     | NULL    |       |
  | name  | varchar(16) | YES  |     | NULL    |       |
  | age   | int         | YES  |     | NULL    |       |
  +-------+-------------+------+-----+---------+-------+
  3 rows in set (0.00 sec)
  
  mysql> alter table t2 drop age;
  Query OK, 0 rows affected (0.08 sec)
  Records: 0  Duplicates: 0  Warnings: 0
  
  mysql> desc t2;
  +-------+-------------+------+-----+---------+-------+
  | Field | Type        | Null | Key | Default | Extra |
  +-------+-------------+------+-----+---------+-------+
  | id    | int         | YES  |     | NULL    |       |
  | name  | varchar(16) | YES  |     | NULL    |       |
  +-------+-------------+------+-----+---------+-------+
  2 rows in set (0.00 sec)
  
  mysql> alter table t2 change name name1 int;
  Query OK, 0 rows affected (0.09 sec)
  Records: 0  Duplicates: 0  Warnings: 0
  
  mysql> desc t2;
  +-------+------+------+-----+---------+-------+
  | Field | Type | Null | Key | Default | Extra |
  +-------+------+------+-----+---------+-------+
  | id    | int  | YES  |     | NULL    |       |
  | name1 | int  | YES  |     | NULL    |       |
  +-------+------+------+-----+---------+-------+
  2 rows in set (0.00 sec)
  
  mysql>
  

• 查

  语法：
  	desc 表1;
  	show tables;
  	show create tables 表名;
  	
  	mysql> desc t1;
      +-------+-------------+------+-----+---------+-------+
      | Field | Type        | Null | Key | Default | Extra |
      +-------+-------------+------+-----+---------+-------+
      | id    | int         | YES  |     | NULL    |       |
      | name  | varchar(16) | YES  |     | NULL    |       |
      +-------+-------------+------+-----+---------+-------+
      2 rows in set (0.01 sec)
      
      mysql> show tables;
      +---------------+
      | Tables_in_db1 |
      +---------------+
      | t2            |
      +---------------+
      1 row in set (0.00 sec)
  
      mysql>
  

  记录的增删改查

  • 增

    1.插入完整数据(顺序插入)
    	insert into 表1(字段1， 字段2) values(值1，值2)
    	insert into 表1 values(值1， 值2)
    2.指定插入数据
    	insert into 表1(字段1) values (值1)
    3.插入多条记录
    	insert into 表1 values
    		(值1， 值2)，
    		(值1， 值2);
    

  • 删

    delete from 表1 where 条件(可以用and或者or连接)
    

  • 改

    update 表1 set 字段1=值1 where 条件；
    

  • 查

    select *from 表1;
    select 字段1，字段2 from 表1;
    

  • mysql> insert into t2(id, name1) values(1, 123);
    Query OK, 1 row affected (0.01 sec)
    
    mysql> show tables;
    +---------------+
    | Tables_in_db1 |
    +---------------+
    | t2            |
    +---------------+
    1 row in set (0.00 sec)
    
    mysql> select * from t2;
    +------+-------+
    | id   | name1 |
    +------+-------+
    |    1 |   123 |
    +------+-------+
    1 row in set (0.00 sec)
    
    mysql> insert into t2 values(2, 23);
    Query OK, 1 row affected (0.01 sec)
    
    mysql> select * from t2;
    +------+-------+
    | id   | name1 |
    +------+-------+
    |    1 |   123 |
    |    2 |    23 |
    +------+-------+
    2 rows in set (0.00 sec)
    
    mysql> insert into t2 values (3, 34), (4, 45);
    Query OK, 2 rows affected (0.01 sec)
    Records: 2  Duplicates: 0  Warnings: 0
    
    mysql> select * from t2;
    +------+-------+
    | id   | name1 |
    +------+-------+
    |    1 |   123 |
    |    2 |    23 |
    |    3 |    34 |
    |    4 |    45 |
    +------+-------+
    4 rows in set (0.00 sec)
    
    mysql> delete from t2 where id=2;
    Query OK, 1 row affected (0.01 sec)
    
    mysql> select * from t2;
    +------+-------+
    | id   | name1 |
    +------+-------+
    |    1 |   123 |
    |    3 |    34 |
    |    4 |    45 |
    +------+-------+
    3 rows in set (0.00 sec)
    
    mysql> update t2 set id =2 where id=3;
    Query OK, 1 row affected (0.01 sec)
    Rows matched: 1  Changed: 1  Warnings: 0
    
    mysql> select * from t2;
    +------+-------+
    | id   | name1 |
    +------+-------+
    |    1 |   123 |
    |    2 |    34 |
    |    4 |    45 |
    +------+-------+
    3 rows in set (0.00 sec)