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Mysql View
醜話說在前面，對於企業級項目是不推薦使用視圖的。但是東西用在合適的地方就是最好的。
參考資料：
視圖簡介
一、爲何使用視圖
- 安全
用戶權限與視圖綁定。實際上可以通過shiro或者spring-security控制。
-
查詢性能提高
-
虛擬表不用修改表結構，可以完成某些業務需求。這一點比較實用。
二、視圖的工作機制
- 視圖的工作機制
當調用視圖的時候，纔會執行視圖中的sql，進行取數據操作。視圖的內容沒有存儲，而是在視圖被引用的時候纔派生出數據。這樣不會佔用空間，由於是即時引用，視圖的內容總是與真實表的內容是一致的。
- 如此設計的優點
節省空間。維護好真實表的內容，就可保證視圖的完整性。
CRUD
爲了測試。創建一個user表。DDL如下：
CREATE TABLE `user` (
`id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主鍵,自增',
`mobile` varchar(20) NOT NULL COMMENT '手機號',
`password` varchar(64) NOT NULL COMMENT '密碼',
`salt` varchar(128) NOT NULL COMMENT '密碼鹽',
`nickname` varchar(32) NOT NULL DEFAULT '' COMMENT '暱稱',
`is_deleted` tinyint(4) NOT NULL DEFAULT '0' COMMENT '是否刪除 {0:未刪除, 1:已刪除}',
`created_time` datetime NOT NULL COMMENT '創建時間',
`updated_time` datetime NOT NULL COMMENT '最後更新時間',
PRIMARY KEY (`id`),
UNIQUE KEY `id_UNIQUE` (`id`),
UNIQUE KEY `mobile_UNIQUE` (`mobile`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='用戶表'
數據初始化：
INSERT INTO `user` (mobile, password, salt, nickname, is_deleted, created_time, updated_time) VALUES ('13062666053', 'a7097b4e5fa3c1d1165e66b2d72a2d060f288d64', '649f6afc93874cf8', '某小寶', 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', '某寶', 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]
假設我們只關心用戶的信息，如下：
CREATE VIEW v_user_info AS SELECT nickname, mobile, is_deleted FROM `user`;
- Read
視圖創建成功之後，可以像普通表一樣對待。
mysql> select * from v_user_info;
+-----------+-------------+------------+
| nickname | mobile | is_deleted |
+-----------+-------------+------------+
| 某小寶 | 13062666053 | 0 |
| 某寶 | 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
對視圖的數據修改會直接反應在真實表之上。
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)
我們也可以修改視圖的結構，就像修改表結構一樣。比如我們不想關心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 | 某小寶 |
| 13012345678 | 某寶 |
| 10123456789 | 11 |
| 13111111112 | 12 |
+-------------+-----------+
4 rows in set (0.00 sec)
- Drop
DROP VIEW VIEW_NAME;
比如我們不想要這張視圖了
mysql> drop view v_user_info;
Query OK, 0 rows affected (0.00 sec)