Mysql DDL语句之视图

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。

创建视图
创建视图
查看视图
修改视图
删除视图

toc

• 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;