MySQL之DDL&DCL&DML
Data Definition Language
1. 库定义
1.1 创建库
- 语法：
CREATE DATABASE awei CHARSET utf8mb4; - 规范
- 库名：小写，业务有关，非数字开头，库名不能太长，不能使用保留字符串
- 必须指定字符集
1.2 查库
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| awei |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
mysql> show create database awei;
+----------+------------------------------------------------------------------+
| Database | Create Database |
+----------+------------------------------------------------------------------+
| awei | CREATE DATABASE `awei` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+----------+------------------------------------------------------------------+
1 row in set (0.00 sec)
1.3 修改库
mysql> alter database awei charset utf8mb4;
Query OK, 1 row affected (0.00 sec)
1.4 删除库
危险，生产环境中，除了管理员，任何人没有删除权限
mysql> drop database awei;
Query OK, 0 rows affected (0.00 sec)
2. 表定义
2.1 创建表
- 规范
- 表名：小写字母，非数字开头，表名与业务有关，表名不能太长，不能使用关键字
- 必须设置存储引擎和字符集
- 数据类型：合适、简短、足够
- 必须有主键
- 每个列尽量设置非空索引，不知道填啥就设定默认值
- 每个列要有注释comment
2.2 查询表
mysql> show tables;
+----------------+
| Tables_in_awei |
+----------------+
| user |
+----------------+
1 row in set (0.00 sec)
mysql> desc user;
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(64) | NO | | NULL | |
| age | tinyint(3) unsigned | NO | | 18 | |
| gender | char(1) | NO | | F | |
| cometime | datetime | NO | | NULL | |
| province | enum('北京市','上海市','广东省','湖南省') | NO | | 广东省 | |
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
6 rows in set (0.03 sec)
mysql> show create table user;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| user | CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(64) NOT NULL,
`age` tinyint(3) unsigned NOT NULL DEFAULT '18',
`gender` char(1) NOT NULL DEFAULT 'F',
`cometime` datetime NOT NULL,
`province` enum('北京市','上海市','广东省','湖南省') NOT NULL DEFAULT '广东省',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)
2.3 修改表
- 添加手机号列
mysql> alter table user add column tel char(11) not null unique key comment '手机号';
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc user;
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(64) | NO | | NULL | |
| age | tinyint(3) unsigned | NO | | 18 | |
| gender | char(1) | NO | | F | |
| cometime | datetime | NO | | NULL | |
| province | enum('北京市','上海市','广东省','湖南省') | NO | | 广东省 | |
| tel | char(11) | NO | UNI | NULL | |
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
7 rows in set (0.00 sec)
- 将手机列的数据类型改成bigint
mysql> alter table user modify tel bigint not null unique key comment '手机号';
Query OK, 0 rows affected, 1 warning (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 1
mysql> desc user;
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(64) | NO | | NULL | |
| age | tinyint(3) unsigned | NO | | 18 | |
| gender | char(1) | NO | | F | |
| cometime | datetime | NO | | NULL | |
| province | enum('北京市','上海市','广东省','湖南省') | NO | | 广东省 | |
| tel | bigint(20) | NO | UNI | NULL | |
+----------+-------------------------------------------------------+------+-----+-----------+----------------+
7 rows in set (0.00 sec)
- 删除手机号列
mysql> alter table user drop tel;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
2.4 删除表
mysql> drop table user;
Data Control Language
MySQL之基础管理
Data Manager Language
1. 作用
对表中的数据行进行操作
2. insert
添加数据
-- 规范用法
DESC user;
INSERT INTO
user(id, sname, age, gender, addr, cometime, telnum)
VALUES(1, '张三', 18, 1, '北京市', '2020-06-13 16:37:00', 110);
-- 简约方法
INSERT INTO
user
VALUES(2, '李四', 20, 1, '北京市', '2020-06-13 16:37:00', 119);
-- 部分录入数据（使用默认值）
INSERT INTO
user(snametelnum)
VALUES('王五', 120);
-- 批量录入数据
INSERT INTO
user(snametelnum)
VALUES('张三', 110), VALUES('李四', 119), VALUES('王五', 120);
3. update
更新数据
-- 必须明确指定要改哪一行，一般update语句都有where条件
UPDATE student SET sname='阿玮' WHERE id = 1;
4. DELETE
删除数据
-- 必须明确指定要删哪一行，一般update语句都有where条件
DELETE from student WHERE id = 1;
4.1 伪删除
-- 修改表结构
ALTER TABLE user ADD COLUMN state TINYINT NOT NULL DEFAULT 1;
-- 删除数据改为update
UPDATE user SET state=0 where id=1;
-- 查询语句修改为
SELECT * FROM user WHERE state=1;
4.2 三种删除语句的区别
-- 以下三条命令都能删除全表数据
delete from user;
-- 逻辑上逐行删除，当数据行较多的时候操作很慢
-- 并没有真正从磁盘上删除，只是在存储层打标记，磁盘空间不立即释放，HWM高水平线不会降低
-- delete属于DML操作，只需要通过反转日志（binlog）就能恢复
drop table user;
-- 将表结构（元数据）和数据行物理层次删除
-- drop属于DDL操作，需要通过备份+日志恢复
truncate table user;
-- 清空表段中的所有数据页，物理层次删除全表数据，磁盘空间会立即释放，HWM高水平线会降低
-- truncate属于DDL操作，需要通过备份+日志恢复