Mysql 视图是一个虚拟表，内容由
select查询语句定义, 同真实的表数据一致, 但是视图并不在数据库中以存储的数据值形式存在。
试图引用自定义查询表的字段, 并且在引用试图时动态生成, 对其所引用的基础表来说 Mysql 视图的作用类似于筛选。
- 定义视图的筛选可以来自当前或其它数据库的一个或多个表，或者其它视图。
- 视图查询没有任何限制，通过它们进行数据修改时的限制也很少。
- 视图是存储在数据库中的 SQL 查询语句，它主要出于两种原因：
- 安全原因, 视图可以隐藏一些敏感的信息。
- 简化查询, 使复杂的查询易于理解和使用
创建视图
创建单表视图环境准备
## 创建表
mysql> use test;
mysql> create table t2(
id int primary key AUTO_INCREMENT not null,
name varchar(30) not null,
sex enum('man','gril') default 'man' not null,
time date not null,
post varchar(50) not null,
job varchar(100),
salary double(15,2) not null,
dep_id int
);
## 插入数据
mysql> insert into t2(name,sex,time,post,job,salary,dep_id) values
('jack','man','20180202','it','teach',5000,100),
('tom','man','20180203','it','teach',5500,100),
('robin','man','20180202','it','teach',8000,100),
('alice','gril','20180202','it','teach',7200,100),
('lisi','man','20180202','hr','hrcc',600,101),
('harry','man','20180202','hr', NULL,6000,101),
('trf','gril','20180206','sale','salecc',20000,102),
('test','gril','20180205','sale','salecc',2200,102),
('dog','man','20180205','sale', NULL,2200,102),
('alex','man','20180205','sale','',2200,102);
## 查看表结构
mysql> desc t2;
+--------+--------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | NULL | |
| sex | enum('man','gril') | NO | | man | |
| time | date | NO | | NULL | |
| post | varchar(50) | NO | | NULL | |
| job | varchar(100) | YES | | NULL | |
| salary | double(15,2) | NO | | NULL | |
| dep_id | int(11) | YES | | NULL | |
+--------+--------------------+------+-----+---------+----------------+
## 查询所有数据
mysql> select * from t2;
+----+-------+------+------------+------+--------+----------+--------+
| id | name | sex | time | post | job | salary | dep_id |
+----+-------+------+------------+------+--------+----------+--------+
| 1 | jack | man | 2018-02-02 | it | teach | 5000.00 | 100 |
| 2 | tom | man | 2018-02-03 | it | teach | 5500.00 | 100 |
| 3 | robin | man | 2018-02-02 | it | teach | 8000.00 | 100 |
| 4 | alice | gril | 2018-02-02 | it | teach | 7200.00 | 100 |
| 5 | lisi | man | 2018-02-02 | hr | hrcc | 600.00 | 101 |
| 6 | harry | man | 2018-02-02 | hr | NULL | 6000.00 | 101 |
| 7 | trf | gril | 2018-02-06 | sale | salecc | 20000.00 | 102 |
| 8 | test | gril | 2018-02-05 | sale | salecc | 2200.00 | 102 |
| 9 | dog | man | 2018-02-05 | sale | NULL | 2200.00 | 102 |
| 10 | alex | man | 2018-02-05 | sale | | 2200.00 | 102 |
+----+-------+------+------------+------+--------+----------+--------+创建单表视图
语法：CREATE VIEW 视图名 AS SELECT 语句;
## 创建视图，只能看到姓名，性别，部门，职责
mysql> create view view_t2 as select name,sex,post,job from test.t2;
## 查看视图表结构
mysql> desc view_t2;
+-------+--------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------------+------+-----+---------+-------+
| name | varchar(30) | NO | | NULL | |
| sex | enum('man','gril') | NO | | man | |
| post | varchar(50) | NO | | NULL | |
| job | varchar(100) | YES | | NULL | |
+-------+--------------------+------+-----+---------+-------+
## 查看视图所有内容
mysql> select * from view_t2;
+-------+------+------+--------+
| name | sex | post | job |
+-------+------+------+--------+
| jack | man | it | teach |
| tom | man | it | teach |
| robin | man | it | teach |
| alice | gril | it | teach |
| lisi | man | hr | hrcc |
| harry | man | hr | NULL |
| trf | gril | sale | salecc |
| test | gril | sale | salecc |
| dog | man | sale | NULL |
| alex | man | sale | |
+-------+------+------+--------+创建多表视图环境准备
mysql> create database shop;
mysql> use shop;
## 创建产品表
mysql> create table product(
id int unsigned auto_increment primary key not null,
name varchar(60) not null,
price double not null
);
## 插入产品数据
mysql> insert into product(name,price) values
('apple',5),
('balane',6),
('pear',7);
## 创建销售表
mysql> create table purchase(
id int unsigned auto_increment primary key not null,
name varchar(60) not null,
quantity int not null default 0,
gen_time datetime not null
);
## 插入销售数据
mysql> insert into purchase(name,quantity,gen_time) values
('apple',7,now()),
('pear',10,now());
## 查询产品卖出金额
mysql> select product.name,product.price,purchase.quantity,product.price * purchase.quantity as total_value from product,purchase where product.name = purchase.name;
+-------+-------+----------+-------------+
| name | price | quantity | total_value |
+-------+-------+----------+-------------+
| apple | 5 | 7 | 35 |
| pear | 7 | 10 | 70 |
+-------+-------+----------+-------------+创建多表视图
创建视图
mysql> create view total_product as select product.name,product.price,purchase.quantity,product.price * purchase.quantity as total from purchase,product where purchase.name = product.name;
## 查询视图数据
mysql> select * from total_product;
+-------+-------+----------+-------+
| name | price | quantity | total |
+-------+-------+----------+-------+
| apple | 5 | 7 | 35 |
| pear | 7 | 10 | 70 |
+-------+-------+----------+-------+
## 再次卖出产品后
mysql> insert into purchase(name,quantity,gen_time) values ('balane',20,now());
## 再次查询视图数据
+--------+-------+----------+-------+
| name | price | quantity | total |
+--------+-------+----------+-------+
| apple | 5 | 7 | 35 |
| balane | 6 | 20 | 120 |
| pear | 7 | 10 | 70 |
+--------+-------+----------+-------+查看视图
- 查看视图名
- SHOW TABLES 视图名;
- 查看视图详细信息
- SHOW TABLE STATUS FROM 视图名G
- 查看视图定义信息
- SHOW CREATE VIEW 视图名G
- 查看视图表结构
- DESC 视图名;
修改视图
语法：ALTER VIEW 视图名 AS 新 SELECT 语句
mysql> use test;
mysql> alter view view_t2 as select name,post,job from test.t2;
mysql> desc view_t2;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| name | varchar(30) | NO | | NULL | |
| post | varchar(50) | NO | | NULL | |
| job | varchar(100) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
mysql> select * from view_t2;
+-------+------+--------+
| name | post | job |
+-------+------+--------+
| jack | it | teach |
| tom | it | teach |
| robin | it | teach |
| alice | it | teach |
| lisi | hr | hrcc |
| harry | hr | NULL |
| trf | sale | salecc |
| test | sale | salecc |
| dog | sale | NULL |
| alex | sale | |
+-------+------+--------+删除视图
语法：DROP VIEW view_name [,view_name]…;
mysql> drop view view_t2;