什么是视图?
一张虚表,和真实的表一样。视图包含一系列带有名称的行和列数据。视图是从一个或多个表中导出来的,我们可以通过insert,update,delete来操作视图。当通过视图看到的数据被修改时,相应的原表的数据也会变化。同时原表发生变化,则这种变化也可以自动反映到视图中。
视图具有以下优点:
视图和表的区别以及联系是什么?
两者的区别:
两者的联系:
视图是在基本表之上建立的表,它的结构和内容都来自于基本表,它依赖基本表存在而存在。一个视图可以对应一个基本表,也可以对应多个基本表。视图是基本的抽象和逻辑意义上建立的关系。
1、创建单表视图
#创建表
mysql> create table t(
-> quantity int,
-> price int
-> );
#插入数据
mysql> insert into t values(3,50);
#创建视图
mysql> create view view_t as select quantity,price,quantity*price as total from t;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from view_t; 查看视图中的数据
+----------+-------+-------+
| quantity | price | total |
+----------+-------+-------+
| 3 | 50 | 150 |
+----------+-------+-------+
1 row in set (0.01 sec)
2、创建多表视图
#创建基本表
mysql> create table student(
-> s_id int(3) primary key,
-> s_name varchar(30),
-> s_age int(3),
-> s_sex varchar(8)
-> );
Query OK, 0 rows affected (0.02 sec)
mysql> create table stu_info(
-> s_id int(3),
-> class varchar(50),
-> addr varchar(100)
-> );
Query OK, 0 rows affected (0.01 sec)
#插入数据
mysql> insert into stu_info values
-> (1,'erban','anhui'),
-> (2,'sanban','chongqing'),
-> (3,'yiban','shandong');
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 0
#创建视图
mysql> create view stu_class(id,name,class) as
-> select student.s_id,student.s_name,stu_info.class
-> from student,stu_info where student.s_id=stu_info.s_id;
3、查看视图的相关信息
#查看视图的表结构
mysql> desc stu_class;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(3) | NO | | NULL | |
| name | varchar(30) | YES | | NULL | |
| class | varchar(50) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
#查看视图的基本信息
mysql> show table status like 'stu_class'\G
*************************** 1. row ***************************
Name: stu_class
Engine: NULL
Version: NULL
Row_format: NULL
Rows: NULL
Avg_row_length: NULL
Data_length: NULL
Max_data_length: NULL
Index_length: NULL
Data_free: NULL
Auto_increment: NULL
Create_time: NULL
Update_time: NULL
Check_time: NULL
Collation: NULL
Checksum: NULL
Create_options: NULL
Comment: VIEW
1 row in set (0.00 sec)
#查看视图的详细信息
mysql> show create view stu_class\G
*************************** 1. row ***************************
View: stu_class
Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `stu_class` AS select `student`.`s_id` AS `id`,`student`.`s_name` AS `name`,`stu_info`.`class` AS `class` from (`student` join `stu_info`) where (`student`.`s_id` = `stu_info`.`s_id`)
character_set_client: utf8
collation_connection: utf8_general_ci
1 row in set (0.00 sec)
#也可以直接查询information_schema库中的views表,来查看所有的视图
mysql> select * from information_schema.views where table_schema='test1'\G
#where后面指定的是一个库名,也就是查看test02这个库中的所有视图
4、修改视图 方法一:
mysql> create or replace view view_t as select * from t;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from view_t; 查看修改后的视图
+----------+-------+
| quantity | price |
+----------+-------+
| 3 | 50 |
+----------+-------+
1 row in set (0.00 sec)
方法二:
#修改指定视图的列名
mysql> alter view view_t(abc) as select quantity from t;
Query OK, 0 rows affected (0.00 sec)
#查看修改后的表结构
mysql> desc view_t;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| abc | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.00 sec)
5、更新视图 1)update指令更新
#查看表以及视图的数据,其中quantity对应视图的abc字段
mysql> select * from t;
+----------+-------+
| quantity | price |
+----------+-------+
| 3 | 50 |
+----------+-------+
1 row in set (0.00 sec)
mysql> select * from view_t;
+------+
| abc |
+------+
| 3 |
+------+
1 row in set (0.01 sec)
mysql> update view_t set abc=5;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
#查看更新后的视图
mysql> select * from view_t;
+------+
| abc |
+------+
| 5 |
+------+
1 row in set (0.00 sec)
#查看更新后的表
mysql> select * from t;
+----------+-------+
| quantity | price |
+----------+-------+
| 5 | 50 |
+----------+-------+
1 row in set (0.00 sec)
2)insert指令更新
#查看表的数据
mysql> select * from t;
+----------+-------+
| quantity | price |
+----------+-------+
| 5 | 50 |
+----------+-------+
1 row in set (0.00 sec)
#查看视图的数据
mysql> select * from view_t;
+------+
| abc |
+------+
| 5 |
+------+
1 row in set (0.00 sec)
#向表中插入数据
mysql> insert into t values(3,5);
Query OK, 1 row affected (0.00 sec)
#查看视图的数据
mysql> select * from view_t;
+------+
| abc |
+------+
| 5 |
| 3 |
+------+
2 rows in set (0.00 sec)
#查看表的数据
mysql> select * from t;
+----------+-------+
| quantity | price |
+----------+-------+
| 5 | 50 |
| 3 | 5 |
+----------+-------+
3) delete指令删除表数据
#创建新的视图
mysql> create view view_t2(qty,price,total) as select quantity,price,quantity*price from t;
mysql> select * from view_t2;
+------+-------+-------+
| qty | price | total |
+------+-------+-------+
| 5 | 50 | 250 |
| 3 | 5 | 15 |
+------+-------+-------+
2 rows in set (0.00 sec)
#删除视图中的数据
mysql> delete from view_t2 where price=5;
Query OK, 1 row affected (0.00 sec)
#再次查看视图的数据
mysql> select * from view_t2;
+------+-------+-------+
| qty | price | total |
+------+-------+-------+
| 5 | 50 | 250 |
+------+-------+-------+
1 row in set (0.00 sec)
查看原表的数据
mysql> select * from t;
+----------+-------+
| quantity | price |
+----------+-------+
| 5 | 50 |
+----------+-------+
1 row in set (0.00 sec)
6、删除视图
mysql> drop view view_t;