mysql视图之管理视图实例详解

本文实例讲述了mysql视图之管理视图操作。分享给大家供大家参考,具体如下:

mysql提供了用于显示视图定义的SHOW CREATE VIEW语句,我们来看下语法结构:

SHOW CREATE VIEW [database_name].[view_ name];

要显示视图的定义,需要在SHOW CREATE VIEW子句之后指定视图的名称,我们先来根据employees表创建一个简单的视图用来显示公司组织结构,完事在进行演示:

CREATE VIEW organization AS
  SELECT 
    CONCAT(E.lastname, E.firstname) AS Employee,
    CONCAT(M.lastname, M.firstname) AS Manager
  FROM
    employees AS E
      INNER JOIN
    employees AS M ON M.employeeNumber = E.ReportsTo
  ORDER BY Manager;

从以上视图中查询数据,得到以下结果:

mysql> SELECT * FROM organization;
+------------------+------------------+
| Employee     | Manager     |
+------------------+------------------+
| BondurLoui    | BondurGerard   |
| CastilloPamela  | BondurGerard   |
| JonesBarry    | BondurGerard   |
| HernandezGerard | BondurGerard   |
.......此处省略了many many数据.......
| KatoYoshimi   | NishiMami    |
| KingTom     | PattersonWilliam |
| MarshPeter    | PattersonWilliam |
| FixterAndy    | PattersonWilliam |
+------------------+------------------+
24 rows in set

要显示视图的定义,请使用SHOW CREATE VIEW语句如下:

SHOW CREATE VIEW organization;

我们还可以使用任何纯文本编辑器(如记事本)显示视图的定义,以打开数据库文件夹中的视图定义文件。例如,要打开organization视图定义,可以在数据库文件夹下的data文件夹中找到你数据库文件夹,完事进入其中按着你视图名称找.frm文件。

我们再来通过ALTER VIEW和CREATE OR REPLACE VIEW来尝试修改视图,先来看下alert view语法:

ALTER
 [ALGORITHM = {MERGE | TEMPTABLE | UNDEFINED}]
 VIEW [database_name]. [view_name]
  AS
 [SELECT statement]

以下语句通过添加email列来演示如何修改organization视图:

ALTER VIEW organization
 AS 
 SELECT CONCAT(E.lastname,E.firstname) AS Employee,
     E.email AS employeeEmail,
     CONCAT(M.lastname,M.firstname) AS Manager
 FROM employees AS E
 INNER JOIN employees AS M
  ON M.employeeNumber = E.ReportsTo
 ORDER BY Manager;

要验证更改,可以从organization视图中查询数据,咱就不赘述了,完事来看下另一个语法结构:

CREATE OR REPLACE VIEW v_contacts AS
  SELECT 
    firstName, lastName, extension, email
  FROM
    employees;
-- 查询视图数据
SELECT * FROM v_contacts;

我们要注意,在我们修改的时候,如果一个视图已经存在,mysql只会修改视图。如果视图不存在,mysql将创建一个新的视图。好啦,我们来看下上述sql执行的结果:

+-----------+-----------+-----------+--------------------------------+
| firstName | lastName | extension | email             |
+-----------+-----------+-----------+--------------------------------+
| Diane   | Murphy  | x5800   | dmurphy@yiibai.com       |
| Mary   | Hill   | x4611   | mary.hill@yiibai.com      |
| Jeff   | Firrelli | x9273   | jfirrelli@yiibai.com      |
| William  | Patterson | x4871   | wpatterson@yiibai.com     |
| Gerard  | Bondur  | x5408   | gbondur@gmail.com       |
| Anthony  | Bow    | x5428   | abow@gmail.com         |
| Leslie  | Jennings | x3291   | ljennings@yiibai.com      |
.............. 此处省略了many many数据 ..................................
| Martin  | Gerard  | x2312   | mgerard@gmail.com       |
| Lily   | Bush   | x9111   | lilybush@yiiibai.com      |
| John   | Minsu   | x9112   | johnminsu@classicmodelcars.com |
+-----------+-----------+-----------+--------------------------------+
25 rows in set

假设我们要将职位(jobtitle)列添加到v_contacts视图中,只需使用以下语句:

CREATE OR REPLACE VIEW v_contacts AS
  SELECT 
    firstName, lastName, extension, email, jobtitle
  FROM
    employees;
-- 查询视图数据
SELECT * FROM v_contacts;

执行上面查询语句后,可以看到添加一列数据:

+-----------+-----------+-----------+--------------------------------+----------------------+
| firstName | lastName | extension | email             | jobtitle       |
+-----------+-----------+-----------+--------------------------------+----------------------+
| Diane   | Murphy  | x5800   | dmurphy@yiibai.com       | President      |
| Mary   | Hill   | x4611   | mary.hill@yiibai.com      | VP Sales       |
| Jeff   | Firrelli | x9273   | jfirrelli@yiibai.com      | VP Marketing     |
................... 此处省略了一大波数据 ....................................................
| Yoshimi  | Kato   | x102   | ykato@gmail.com        | Sales Rep      |
| Martin  | Gerard  | x2312   | mgerard@gmail.com       | Sales Rep      |
| Lily   | Bush   | x9111   | lilybush@yiiibai.com      | IT Manager      |
| John   | Minsu   | x9112   | johnminsu@classicmodelcars.com | SVP Marketing    |
+-----------+-----------+-----------+--------------------------------+----------------------+
25 rows in set

完事我们来看使用DROP VIEW语句将视图删除,先来看下语法结构:

DROP VIEW [IF EXISTS] [database_name].[view_name]

上述sql中,IF EXISTS是语句的可选子句,它允许我们检查视图是否存在,用来避免删除不存在的视图的错误。完事我们来删除organization视图:

DROP VIEW IF EXISTS organization;

我们得注意下,每次修改或删除视图时,mysql会将视图定义文件备份到/database_name/arc/内容介绍中。 如果我们意外修改或删除视图,可以从/database_name/arc/文件夹获取其备份。

好啦,本次记录就到这里了。

更多关于MySQL相关内容感兴趣的读者可查看本站专题:《MySQL查询技巧大全》、《MySQL事务操作技巧汇总》、《MySQL存储过程技巧大全》、《MySQL数据库锁相关技巧汇总》及《MySQL常用函数大汇总》

希望本文所述对大家MySQL数据库计有所帮助。

共享资源网提供最优质的资源集合。
共享资源网 » mysql视图之管理视图实例详解

共享资源网提供最优质的资源集合

充值中心 开启会员