MySQL View 视图
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Mysql View
丑话说在前面，对于企业级项目是不推荐使用视图的。但是东西用在合适的地方就是最好的。
参考资料：
视图简介
一、为何使用视图
- 安全
用户权限与视图绑定。实际上可以通过shiro或者spring-security控制。
-
查询性能提高
-
虚拟表不用修改表结构，可以完成某些业务需求。这一点比较实用。
二、视图的工作机制
- 视图的工作机制
当调用视图的时候，才会执行视图中的sql，进行取数据操作。视图的内容没有存储，而是在视图被引用的时候才派生出数据。这样不会占用空间，由于是即时引用，视图的内容总是与真实表的内容是一致的。
- 如此设计的优点
节省空间。维护好真实表的内容，就可保证视图的完整性。
CRUD
为了测试。创建一个user表。DDL如下：
CREATE TABLE `user` (
`id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键,自增',
`mobile` varchar(20) NOT NULL COMMENT '手机号',
`password` varchar(64) NOT NULL COMMENT '密码',
`salt` varchar(128) NOT NULL COMMENT '密码盐',
`nickname` varchar(32) NOT NULL DEFAULT '' COMMENT '昵称',
`is_deleted` tinyint(4) NOT NULL DEFAULT '0' COMMENT '是否删除 {0:未删除, 1:已删除}',
`created_time` datetime NOT NULL COMMENT '创建时间',
`updated_time` datetime NOT NULL COMMENT '最后更新时间',
PRIMARY KEY (`id`),
UNIQUE KEY `id_UNIQUE` (`id`),
UNIQUE KEY `mobile_UNIQUE` (`mobile`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='用户表'
数据初始化：
INSERT INTO `user` (mobile, password, salt, nickname, is_deleted, created_time, updated_time) VALUES ('13062666053', 'a7097b4e5fa3c1d1165e66b2d72a2d060f288d64', '649f6afc93874cf8', '某小宝', 0, '2016-09-17 14:08:38', '2016-09-17 14:08:38');
INSERT INTO `user` (mobile, password, salt, nickname, is_deleted, created_time, updated_time) VALUES ('13012345678', '67917009d2faccc292171bb16084d7410616cdcb', '7c3186569813f1c3', '某宝', 0, '2016-09-17 14:08:38', '2016-09-17 14:08:38');
INSERT INTO `user` (mobile, password, salt, nickname, is_deleted, created_time, updated_time) VALUES ('13111111111', '847100b326a0574c0cdcc22483e13cb39accdefd', '48c3e9cfac9ac472', '11', 0, '2016-09-17 18:29:25', '2016-09-17 18:29:25');
INSERT INTO `user` (mobile, password, salt, nickname, is_deleted, created_time, updated_time) VALUES ('13111111112', '1d4fe693d850b2e5de5f348c69bfe15a78249022', 'c1d2a40cd8db1a88', '12', 0, '2016-09-17 18:30:10', '2016-09-17 18:30:10')
- Create
CREATE [OR REPLACE] [ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}]
VIEW view_name [(column_list)]
AS select_statement
[WITH [CASCADED | LOCAL] CHECK OPTION]
假设我们只关心用户的信息，如下：
CREATE VIEW v_user_info AS SELECT nickname, mobile, is_deleted FROM `user`;
- Read
视图创建成功之后，可以像普通表一样对待。
mysql> select * from v_user_info;
+-----------+-------------+------------+
| nickname | mobile | is_deleted |
+-----------+-------------+------------+
| 某小宝 | 13062666053 | 0 |
| 某宝 | 13012345678 | 0 |
| 11 | 13111111111 | 0 |
| 12 | 13111111112 | 0 |
+-----------+-------------+------------+
4 rows in set (0.00 sec)
mysql> desc v_user_info;
+------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| nickname | varchar(32) | NO | | | |
| mobile | varchar(20) | NO | | NULL | |
| is_deleted | tinyint(4) | NO | | 0 | |
+------------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
- Update
对视图的数据修改会直接反应在真实表之上。
mysql> select * from user where nickname='11';
+----+-------------+------------------------------------------+------------------+----------+------------+---------------------+---------------------+
| id | mobile | password | salt | nickname | is_deleted | created_time | updated_time |
+----+-------------+------------------------------------------+------------------+----------+------------+---------------------+---------------------+
| 5 | 13111111111 | 847100b326a0574c0cdcc22483e13cb39accdefd | 48c3e9cfac9ac472 | 11 | 0 | 2016-09-17 18:29:25 | 2016-09-17 18:29:25 |
+----+-------------+------------------------------------------+------------------+----------+------------+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> update v_user_info set mobile='10123456789' where nickname='11';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from user where nickname='11';
+----+-------------+------------------------------------------+------------------+----------+------------+---------------------+---------------------+
| id | mobile | password | salt | nickname | is_deleted | created_time | updated_time |
+----+-------------+------------------------------------------+------------------+----------+------------+---------------------+---------------------+
| 5 | 10123456789 | 847100b326a0574c0cdcc22483e13cb39accdefd | 48c3e9cfac9ac472 | 11 | 0 | 2016-09-17 18:29:25 | 2016-09-17 18:29:25 |
+----+-------------+------------------------------------------+------------------+----------+------------+---------------------+---------------------+
1 row in set (0.00 sec)
我们也可以修改视图的结构，就像修改表结构一样。比如我们不想关心is_deleted了。
mysql> alter view v_user_info AS SELECT mobile, nickname FROM user;
Query OK, 0 rows affected (0.01 sec)
mysql> select * from v_user_info;
+-------------+-----------+
| mobile | nickname |
+-------------+-----------+
| 13062666053 | 某小宝 |
| 13012345678 | 某宝 |
| 10123456789 | 11 |
| 13111111112 | 12 |
+-------------+-----------+
4 rows in set (0.00 sec)
- Drop
DROP VIEW VIEW_NAME;
比如我们不想要这张视图了
mysql> drop view v_user_info;
Query OK, 0 rows affected (0.00 sec)