MySQL:视图

/*样例表*/
CREATE TABLE student
(
  s_id  INT,
  name  VARCHAR(40)
);

CREATE TABLE stu_info
(
  s_id   INT,
  glass  VARCHAR(40),
  addr   VARCHAR(90)
);

【例11.1】在t表格上创建一个名为view_t的视图，代码如下：
CREATE TABLE t (qty INT, price INT);         /*创建基本表t*/
INSERT INTO t VALUES(3, 50);                 /*插入记录*/
CREATE VIEW view_t AS SELECT quantity, price, quantity *price FROM t;    /*创建视图view_t*/
SELECT * FROM view_t;


【例11.2】在t表格上创建一个名为view_t2的视图，代码如下：
CREATE VIEW view_t2(qty, price, total ) AS SELECT quantity, price, quantity *price FROM t;
SELECT * FROM view_t2;


【例11.3】在表student和表stu_info上创建视图stu_glass，代码如下：
INSERT INTO student VALUES(1,'wanglin1'),(2,'gaoli'),(3,'zhanghai');                /*插入记录*/
INSERT INTO stu_info VALUES(1, 'wuban','henan'),(2,'liuban','hebei'),(3,'qiban','shandong');

CREATE VIEW stu_glass (id,name, glass) AS SELECT student.s_id,student.name ,stu_info.glass FROM student ,stu_info WHERE student.s_id=stu_info.s_id;

SELECT * FROM stu_glass;


【例11.4】通过DESCRIBE语句查看视图view_t的定义，代码如下：
DESCRIBE view_t;


【例11.5】下面将通过一个例子来学习使用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;

【例11.6】SHOW CREATE VIEW查看视图的详细定义，代码如下：
SHOW CREATE VIEW view_t \G;


【例11.7】在views表中查看视图的详细定义，代码如下：
SELECT * FROM information_schema.views \G;


【例11.8】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;

【例11.9】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;

【例11.10】使用UPDATE语句更新视图view_t，代码如下：
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;

【例11.11】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;

【例11.12】删除stu_glass视图，代码如下：
DROP VIEW IF EXISTS stu_glass;
SHOW CREATE VIEW stu_glass;

综合案例

步骤1：创建学生表stu，插入3条记录。
CREATE TABLE stu
(
s_id INT PRIMARY KEY,
s_name VARCHAR(20),
addr VARCHAR(50),
tel VARCHAR(50)
);
INSERT INTO stu
VALUES(1,'XiaoWang','Henan','0371-12345678'),
(2,'XiaoLi','Hebei','13889072345'),
(3,'XiaoTian','Henan','0371-12345670');


步骤2：创建报名表sign，插入3条记录。
CREATE TABLE sign
(
s_id INT PRIMARY KEY,
s_name VARCHAR(20),
s_sch VARCHAR(50),
s_sign_sch VARCHAR(50)
);
INSERT INTO sign
VALUES(1,'XiaoWang','Middle School1','Peking University'),
(2,'XiaoLi','Middle School2','Tsinghua University'),
(3,'XiaoTian','Middle School3','Tsinghua University');


步骤3：创建成绩表stu_mark，插入3条记录。
CREATE TABLE stu_mark (s_id INT PRIMARY KEY ,s_name VARCHAR(20) ,mark int );
INSERT INTO stu_mark VALUES(1,'XiaoWang',80),(2,'XiaoLi',71),(3,'XiaoTian',70);


步骤4：创建考上Peking University的学生的视图
CREATE VIEW beida (id,name,mark,sch)
AS SELECT stu_mark.s_id,stu_mark.s_name,stu_mark.mark, sign.s_sign_sch
FROM stu_mark ,sign
WHERE stu_mark.s_id=sign.s_id AND stu_mark.mark>=41 AND sign.s_sign_sch='Peking University';


步骤5：创建考上Tsinghua University的学生的视图
CREATE VIEW qinghua (id,name,mark,sch)
AS SELECT stu_mark.s_id, stu_mark.s_name, stu_mark.mark, sign.s_sign_sch
FROM stu_mark ,sign
WHERE stu_mark.s_id=sign.s_id  AND stu_mark.mark>=40 AND sign.s_sign_sch='Tsinghua University';



步骤6：XiaoTian的成绩在录入的时候录入错误多录了50分，对其录入成绩进行更正。
UPDATE stu_mark SET mark = mark-50 WHERE stu_mark.s_name ='XiaoTian';


步骤7：查看更新过后视图和表的情况。
SELECT * FROM stu_mark;
SELECT * FROM qinghua;
SELECT * FROM beida;

步骤8：查看视图的创建信息。
 SELECT * FROM information_schema.views\G


步骤9：删除创建的视图。
DROP VIEW beida;
DROP VIEW qinghua;