MySQL 视图简述

单表视图

# 原始表
CREATE TABLE t (quantity INT, price INT);  
INSERT INTO t VALUES(3, 50);  
INSERT INTO t VALUES(5, 560); 

# 基于原始表，创建视图：view_t             
CREATE VIEW view_t AS SELECT quantity, price, quantity *price total FROM t;    

#仅一个查询，就获得乘积
SELECT * FROM view_t;

#基于原始表，创建视图：view_t2
CREATE VIEW view_t2(quantity, price, minus ) AS SELECT quantity, price, quantity - price FROM t;

#仅一个查询就获得差值
SELECT * FROM view_t2;

多表视图

是一张虚拟表，操作上与真实表一样
作用：类似存储过程，简化操作

#示例数据表
CREATE TABLE student
(
  s_id  INT,
  name  VARCHAR(40)
);

CREATE TABLE stu_info
(
  s_id   INT,
  glass  VARCHAR(40),
  addr   VARCHAR(90)
);
INSERT INTO student VALUES(1,'wanglin1'),(2,'gaoli'),(3,'zhanghai');    
INSERT INTO stu_info VALUES(1, 'wuban','henan'),(2,'liuban','hebei'),(3,'qiban','shandong');

#在表student和表stu_info上创建视图stu_glass，展示分班信息：id，姓名，班级：
CREATE VIEW stu_glass 
AS SELECT student.s_id id,student.name name,stu_info.glass glass 
FROM student ,stu_info 
WHERE student.s_id=stu_info.s_id;

SELECT * FROM stu_glass;

查看视图

DESCRIBE view_t;


#SHOW TABLE STATUS命令查看视图信息，代码如下：
SHOW TABLE STATUS LIKE 'view_t' \G;
SHOW TABLE STATUS LIKE 't' \G;

#SHOW CREATE VIEW查看视图的详细定义，代码如下：
SHOW CREATE VIEW view_t \G;


#在views表中查看视图的详细定义，代码如下：
SELECT * FROM information_schema.views \G;

修改视图

#修改视图view_t，代码如下：
DESC view_t;
CREATE OR REPLACE VIEW view_t AS SELECT * FROM t;
DESC view_t;

#使用ALTER语句修改视图view_t，代码如下：
DESC view_t;
ALTER VIEW view_t AS SELECT quantity FROM t; 
DESC view_t;

更新视图

• 实际上是对原始表的更新，会对基于原始表的所有视图产生影响

#使用UPDATE语句更新视图view_t：
SELECT * FROM view_t;          /*查看更新之前的视图*/
SELECT * FROM t;               /*查看更新之前的表*/
UPDATE view_t SET quantity=5;  /*更新视图*/
SELECT * FROM t;               /*查看更新之后的表*/
SELECT * FROM view_t;          /*查看更新之后的视图*/
SELECT * FROM view_t2;

# 从视图插入时注意：含运算列，不能插入，如下语句，不能插入：
INSERT INTO view_t VALUES (3,5);

# 使用INSERT语句在基本表t中插入一条记录，代码如下：
INSERT INTO t VALUES (3,5);
SELECT * FROM t;
SELECT * FROM view_t2;

# 删除stu_glass视图，代码如下：
DROP VIEW IF EXISTS stu_glass;
SHOW CREATE VIEW stu_glass;