数据定义语言(DDL)
- 创建表 create
- 删除表 drop
- 修改表 alter
- 清空表 truncate 彻底清空 无法找回
show databases; ### 查看所有 数据库
show tables; ### 查看所有 表
create database db1 default character set utf8; ### 创建 数据库db1
drop database db1; ### 删除 数据库db1
create table t1(id int(3),name varchar(20)); ### 创建 表t1
insert into t1 values(1,'user1'); ### 插入 数据
desc t1; ### 查看 表结构
alter table t1 add(age int(3)); ### 新增 表字段
alter table t1 drop id; ### 删除 表字段
alter table t1 change age plage int(3); ### 修改 表字段 名称
alter table t1 rname per; ### 修改 表名
truncate table t1; ### 清空 表数据
drop table t1; ### 删除 表
操作
mysql> create database db1 default character set utf8;
Query OK, 1 row affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| db1 |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
mysql> use db1;
Database changed
mysql> show tables;
Empty set (0.00 sec)
mysql> create table t1(id int(3),name varchar(20));
Query OK, 0 rows affected (0.01 sec)
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| t1 |
+---------------+
1 row in set (0.00 sec)
mysql> insert into t1 values(1,'user1');
Query OK, 1 row affected (0.03 sec)
mysql> select * from t1;
+------+-------+
| id | name |
+------+-------+
| 1 | user1 |
+------+-------+
1 row in set (0.00 sec)
mysql> desc t1;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(3) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> alter table t1 add(age int(3));
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t1;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(3) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| age | int(3) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> select * from t1;
+------+-------+------+
| id | name | age |
+------+-------+------+
| 1 | user1 | NULL |
+------+-------+------+
1 row in set (0.00 sec)
mysql> insert into t1 values(1,'user1',10);
Query OK, 1 row affected (0.01 sec)
mysql> truncate table t1;
Query OK, 0 rows affected (0.01 sec)
mysql> drop table t1;
Query OK, 0 rows affected (0.01 sec)
mysql> show tables;
Empty set (0.00 sec)