mysql视图概要
MySql视图
视图是在mysql5之后出现的，是一种虚拟表，行和列的数据来自于定义视图时使用的一些表中，视图的数据是在使用视图的时候动态生成的，视图只保存了sql的逻辑，不保存查询的结果。
5.7伴随的新特性还有虚拟列
虚拟列跟视图的区别：
虚拟列：一个或多个字段的数据函数处理后的结果集映射成的字段
视图：一个或多个表依照某个条件组合而成的结果集（相当于一个查询sql语句的结果集映射成的虚拟表）
其本质其实都是以空间换时间
什么是视图？做什么用？
视图（view）是一种虚拟存在的表，是一个逻辑表，本身并不包含数据。作为一个select语句保存在数据字典中的。
通过视图，可以展现基表的部分数据；视图数据来自定义视图的查询中使用的表，使用视图动态生成。
基表：用来创建视图的表叫做基表base table
数据库中只存放了视图的定义，并没有存放视图中的数据，这些数据都存放在定义视图查询所引用的真实表中。使用视图查询数据时，数据库会从真实表中取出对应的数据。因此，视图中的数据是依赖于真实表中的数据的。一旦真实表中的数据发生改变，显示在视图中的数据也会发生改变。
优点:
1）简单：使用视图的用户完全不需要关心后面对应的表的结构、关联条件和筛选条件，对用户来说已经是过滤好的复合条件的结果集。
2）安全：使用视图的用户只能访问他们被允许查询的结果集，对表的权限管理并不能限制到某个行某个列，但是通过视图就可以简单的实现。
3）数据独立：一旦视图的结构确定了，可以屏蔽表结构变化对用户的影响，源表增加列对视图没有影响；源表修改列名，则可以通过修改视图来解决，不会造成对访问者的影响。
简单来说就是简化了复杂sql操作，不用知道他的查询细节；同时隔离了原始表，可以让使用视图的人不比去接触原始表。保护了数据，提高了安全性。
使用场景
多个地方使用到同样的查询结果，并且该查询结果比较复杂的时候，我们可以使用视图来隐藏复杂的实现细节。
比如某个电商库，各个领导之间权利范围不同，应该看到的东西也不同，领导们指向看到某些指标，不想让你把sql给他去查。况且我们也不会想让数据库的相关信息暴露。
这时用视图隐藏这些sql查询细节
视图和表的区别
| 语法 | 实际中是否占用物理内存 | 使用 | |
|---|---|---|---|
| 视图 | create view | 只保存sql逻辑 | 增删改查，实际上我们只使用查询 |
| 表 | create table | 保存数据 | 增删改查 |
操作示例：
准备测试数据
[root@localhost ~]# wget https://files.cnblogs.com/files/shipment/employees.zip
[root@localhost ~]# unzip employees.zip
Archive: employees.zip
inflating: employees.sql
mysql> source employees.sql;
mysql> use employees
Database changed
mysql> show tables;
+---------------------+
| Tables_in_employees |
+---------------------+
| departments |
| employees |
| job_grades |
| jobs |
| locations |
+---------------------+
5 rows in set (0.00 sec)
或者复制下面的保存到文本，在导入到库
drop database if exists `employees`;
create database `employees`;
USE `employees`;
/*部门表*/
DROP TABLE IF EXISTS `departments`;
CREATE TABLE `departments` (
`department_id` int(4) NOT NULL AUTO_INCREMENT comment '部门id',
`department_name` varchar(3) DEFAULT NULL comment '部门名称',
`manager_id` int(6) DEFAULT NULL comment '管理者id',
`location_id` int(4) DEFAULT NULL comment '部门位置id，来源于表locations中的location_id',
PRIMARY KEY (`department_id`),
KEY `loc_id_fk` (`location_id`)
) ENGINE=InnoDB AUTO_INCREMENT=271 comment '部门表';
insert into `departments`(`department_id`,`department_name`,`manager_id`,`location_id`) values (10,'Adm',200,1700),(20,'Mar',201,1800),(30,'Pur',114,1700),(40,'Hum',203,2400),(50,'Shi',121,1500),(60,'IT',103,1400),(70,'Pub',204,2700),(80,'Sal',145,2500),(90,'Exe',100,1700),(100,'Fin',108,1700),(110,'Acc',205,1700),(120,'Tre',NULL,1700),(130,'Cor',NULL,1700),(140,'Con',NULL,1700),(150,'Sha',NULL,1700),(160,'Ben',NULL,1700),(170,'Man',NULL,1700),(180,'Con',NULL,1700),(190,'Con',NULL,1700),(200,'Ope',NULL,1700),(210,'IT ',NULL,1700),(220,'NOC',NULL,1700),(230,'IT ',NULL,1700),(240,'Gov',NULL,1700),(250,'Ret',NULL,1700),(260,'Rec',NULL,1700),(270,'Pay',NULL,1700);
/*员工表*/
DROP TABLE IF EXISTS `employees`;
CREATE TABLE `employees` (
`employee_id` int(6) NOT NULL AUTO_INCREMENT comment '员工id',
`first_name` varchar(20) DEFAULT NULL comment '名',
`last_name` varchar(25) DEFAULT NULL comment '姓',
`email` varchar(25) DEFAULT NULL comment '电子邮箱',
`phone_number` varchar(20) DEFAULT NULL comment '手机',
`job_id` varchar(10) DEFAULT NULL comment '职位id，来源于jobs表中的job_id',
`salary` double(10,2) DEFAULT NULL comment '薪水',
`commission_pct` double(4,2) DEFAULT NULL comment '佣金百分比',
`manager_id` int(6) DEFAULT NULL comment '上级id',
`department_id` int(4) DEFAULT NULL comment '所属部门id，来源于departments中的department_id',
`hiredate` datetime DEFAULT NULL comment '入职日期',
PRIMARY KEY (`employee_id`)
) ENGINE=InnoDB AUTO_INCREMENT=207 comment '员工表';
insert into `employees`(`employee_id`,`first_name`,`last_name`,`email`,`phone_number`,`job_id`,`salary`,`commission_pct`,`manager_id`,`department_id`,`hiredate`) values (100,'Steven','K_ing','SKING','515.123.4567','AD_PRES',24000.00,NULL,NULL,90,'1992-04-03 00:00:00'),(101,'Neena','Kochhar','NKOCHHAR','515.123.4568','AD_VP',17000.00,NULL,100,90,'1992-04-03 00:00:00'),(102,'Lex','De Haan','LDEHAAN','515.123.4569','AD_VP',17000.00,NULL,100,90,'1992-04-03 00:00:00'),(103,'Alexander','Hunold','AHUNOLD','590.423.4567','IT_PROG',9000.00,NULL,102,60,'1992-04-03 00:00:00'),(104,'Bruce','Ernst','BERNST','590.423.4568','IT_PROG',6000.00,NULL,103,60,'1992-04-03 00:00:00'),(105,'David','Austin','DAUSTIN','590.423.4569','IT_PROG',4800.00,NULL,103,60,'1998-03-03 00:00:00'),(106,'Valli','Pataballa','VPATABAL','590.423.4560','IT_PROG',4800.00,NULL,103,60,'1998-03-03 00:00:00'),(107,'Diana','Lorentz','DLORENTZ','590.423.5567','IT_PROG',4200.00,NULL,103,60,'1998-03-03 00:00:00'),(108,'Nancy','Greenberg','NGREENBE','515.124.4569','FI_MGR',12000.00,NULL,101,100,'1998-03-03 00:00:00'),(109,'Daniel','Faviet','DFAVIET','515.124.4169','FI_ACCOUNT',9000.00,NULL,108,100,'1998-03-03 00:00:00'),(110,'John','Chen','JCHEN','515.124.4269','FI_ACCOUNT',8200.00,NULL,108,100,'2000-09-09 00:00:00'),(111,'Ismael','Sciarra','ISCIARRA','515.124.4369','FI_ACCOUNT',7700.00,NULL,108,100,'2000-09-09 00:00:00'),(112,'Jose Manuel','Urman','JMURMAN','515.124.4469','FI_ACCOUNT',7800.00,NULL,108,100,'2000-09-09 00:00:00'),(113,'Luis','Popp','LPOPP','515.124.4567','FI_ACCOUNT',6900.00,NULL,108,100,'2000-09-09 00:00:00'),(114,'Den','Raphaely','DRAPHEAL','515.127.4561','PU_MAN',11000.00,NULL,100,30,'2000-09-09 00:00:00'),(115,'Alexander','Khoo','AKHOO','515.127.4562','PU_CLERK',3100.00,NULL,114,30,'2000-09-09 00:00:00'),(116,'Shelli','Baida','SBAIDA','515.127.4563','PU_CLERK',2900.00,NULL,114,30,'2000-09-09 00:00:00'),(117,'Sigal','Tobias','STOBIAS','515.127.4564','PU_CLERK',2800.00,NULL,114,30,'2000-09-09 00:00:00'),(118,'Guy','Himuro','GHIMURO','515.127.4565','PU_CLERK',2600.00,NULL,114,30,'2000-09-09 00:00:00'),(119,'Karen','Colmenares','KCOLMENA','515.127.4566','PU_CLERK',2500.00,NULL,114,30,'2000-09-09 00:00:00'),(120,'Matthew','Weiss','MWEISS','650.123.1234','ST_MAN',8000.00,NULL,100,50,'2004-02-06 00:00:00'),(121,'Adam','Fripp','AFRIPP','650.123.2234','ST_MAN',8200.00,NULL,100,50,'2004-02-06 00:00:00'),(122,'Payam','Kaufling','PKAUFLIN','650.123.3234','ST_MAN',7900.00,NULL,100,50,'2004-02-06 00:00:00'),(123,'Shanta','Vollman','SVOLLMAN','650.123.4234','ST_MAN',6500.00,NULL,100,50,'2004-02-06 00:00:00'),(124,'Kevin','Mourgos','KMOURGOS','650.123.5234','ST_MAN',5800.00,NULL,100,50,'2004-02-06 00:00:00'),(125,'Julia','Nayer','JNAYER','650.124.1214','ST_CLERK',3200.00,NULL,120,50,'2004-02-06 00:00:00'),(126,'Irene','Mikkilineni','IMIKKILI','650.124.1224','ST_CLERK',2700.00,NULL,120,50,'2004-02-06 00:00:00'),(127,'James','Landry','JLANDRY','650.124.1334','ST_CLERK',2400.00,NULL,120,50,'2004-02-06 00:00:00'),(128,'Steven','Markle','SMARKLE','650.124.1434','ST_CLERK',2200.00,NULL,120,50,'2004-02-06 00:00:00'),(129,'Laura','Bissot','LBISSOT','650.124.5234','ST_CLERK',3300.00,NULL,121,50,'2004-02-06 00:00:00'),(130,'Mozhe','Atkinson','MATKINSO','650.124.6234','ST_CLERK',2800.00,NULL,121,50,'2004-02-06 00:00:00'),(131,'James','Marlow','JAMRLOW','650.124.7234','ST_CLERK',2500.00,NULL,121,50,'2004-02-06 00:00:00'),(132,'TJ','Olson','TJOLSON','650.124.8234','ST_CLERK',2100.00,NULL,121,50,'2004-02-06 00:00:00'),(133,'Jason','Mallin','JMALLIN','650.127.1934','ST_CLERK',3300.00,NULL,122,50,'2004-02-06 00:00:00'),(134,'Michael','Rogers','MROGERS','650.127.1834','ST_CLERK',2900.00,NULL,122,50,'2002-12-23 00:00:00'),(135,'Ki','Gee','KGEE','650.127.1734','ST_CLERK',2400.00,NULL,122,50,'2002-12-23 00:00:00'),(136,'Hazel','Philtanker','HPHILTAN','650.127.1634','ST_CLERK',2200.00,NULL,122,50,'2002-12-23 00:00:00'),(137,'Renske','Ladwig','RLADWIG','650.121.1234','ST_CLERK',3600.00,NULL,123,50,'2002-12-23 00:00:00'),(138,'Stephen','Stiles','SSTILES','650.121.2034','ST_CLERK',3200.00,NULL,123,50,'2002-12-23 00:00:00'),(139,'John','Seo','JSEO','650.121.2019','ST_CLERK',2700.00,NULL,123,50,'2002-12-23 00:00:00'),(140,'Joshua','Patel','JPATEL','650.121.1834','ST_CLERK',2500.00,NULL,123,50,'2002-12-23 00:00:00'),(141,'Trenna','Rajs','TRAJS','650.121.8009','ST_CLERK',3500.00,NULL,124,50,'2002-12-23 00:00:00'),(142,'Curtis','Davies','CDAVIES','650.121.2994','ST_CLERK',3100.00,NULL,124,50,'2002-12-23 00:00:00'),(143,'Randall','Matos','RMATOS','650.121.2874','ST_CLERK',2600.00,NULL,124,50,'2002-12-23 00:00:00'),(144,'Peter','Vargas','PVARGAS','650.121.2004','ST_CLERK',2500.00,NULL,124,50,'2002-12-23 00:00:00'),(145,'John','Russell','JRUSSEL','011.44.1344.429268','SA_MAN',14000.00,0.40,100,80,'2002-12-23 00:00:00'),(146,'Karen','Partners','KPARTNER','011.44.1344.467268','SA_MAN',13500.00,0.30,100,80,'2002-12-23 00:00:00'),(147,'Alberto','Errazuriz','AERRAZUR','011.44.1344.429278','SA_MAN',12000.00,0.30,100,80,'2002-12-23 00:00:00'),(148,'Gerald','Cambrault','GCAMBRAU','011.44.1344.619268','SA_MAN',11000.00,0.30,100,80,'2002-12-23 00:00:00'),(149,'Eleni','Zlotkey','EZLOTKEY','011.44.1344.429018','SA_MAN',10500.00,0.20,100,80,'2002-12-23 00:00:00'),(150,'Peter','Tucker','PTUCKER','011.44.1344.129268','SA_REP',10000.00,0.30,145,80,'2014-03-05 00:00:00'),(151,'David','Bernstein','DBERNSTE','011.44.1344.345268','SA_REP',9500.00,0.25,145,80,'2014-03-05 00:00:00'),(152,'Peter','Hall','PHALL','011.44.1344.478968','SA_REP',9000.00,0.25,145,80,'2014-03-05 00:00:00'),(153,'Christopher','Olsen','COLSEN','011.44.1344.498718','SA_REP',8000.00,0.20,145,80,'2014-03-05 00:00:00'),(154,'Nanette','Cambrault','NCAMBRAU','011.44.1344.987668','SA_REP',7500.00,0.20,145,80,'2014-03-05 00:00:00'),(155,'Oliver','Tuvault','OTUVAULT','011.44.1344.486508','SA_REP',7000.00,0.15,145,80,'2014-03-05 00:00:00'),(156,'Janette','K_ing','JKING','011.44.1345.429268','SA_REP',10000.00,0.35,146,80,'2014-03-05 00:00:00'),(157,'Patrick','Sully','PSULLY','011.44.1345.929268','SA_REP',9500.00,0.35,146,80,'2014-03-05 00:00:00'),(158,'Allan','McEwen','AMCEWEN','011.44.1345.829268','SA_REP',9000.00,0.35,146,80,'2014-03-05 00:00:00'),(159,'Lindsey','Smith','LSMITH','011.44.1345.729268','SA_REP',8000.00,0.30,146,80,'2014-03-05 00:00:00'),(160,'Louise','Doran','LDORAN','011.44.1345.629268','SA_REP',7500.00,0.30,146,80,'2014-03-05 00:00:00'),(161,'Sarath','Sewall','SSEWALL','011.44.1345.529268','SA_REP',7000.00,0.25,146,80,'2014-03-05 00:00:00'),(162,'Clara','Vishney','CVISHNEY','011.44.1346.129268','SA_REP',10500.00,0.25,147,80,'2014-03-05 00:00:00'),(163,'Danielle','Greene','DGREENE','011.44.1346.229268','SA_REP',9500.00,0.15,147,80,'2014-03-05 00:00:00'),(164,'Mattea','Marvins','MMARVINS','011.44.1346.329268','SA_REP',7200.00,0.10,147,80,'2014-03-05 00:00:00'),(165,'David','Lee','DLEE','011.44.1346.529268','SA_REP',6800.00,0.10,147,80,'2014-03-05 00:00:00'),(166,'Sundar','Ande','SANDE','011.44.1346.629268','SA_REP',6400.00,0.10,147,80,'2014-03-05 00:00:00'),(167,'Amit','Banda','ABANDA','011.44.1346.729268','SA_REP',6200.00,0.10,147,80,'2014-03-05 00:00:00'),(168,'Lisa','Ozer','LOZER','011.44.1343.929268','SA_REP',11500.00,0.25,148,80,'2014-03-05 00:00:00'),(169,'Harrison','Bloom','HBLOOM','011.44.1343.829268','SA_REP',10000.00,0.20,148,80,'2014-03-05 00:00:00'),(170,'Tayler','Fox','TFOX','011.44.1343.729268','SA_REP',9600.00,0.20,148,80,'2014-03-05 00:00:00'),(171,'William','Smith','WSMITH','011.44.1343.629268','SA_REP',7400.00,0.15,148,80,'2014-03-05 00:00:00'),(172,'Elizabeth','Bates','EBATES','011.44.1343.529268','SA_REP',7300.00,0.15,148,80,'2014-03-05 00:00:00'),(173,'Sundita','Kumar','SKUMAR','011.44.1343.329268','SA_REP',6100.00,0.10,148,80,'2014-03-05 00:00:00'),(174,'Ellen','Abel','EABEL','011.44.1644.429267','SA_REP',11000.00,0.30,149,80,'2014-03-05 00:00:00'),(175,'Alyssa','Hutton','AHUTTON','011.44.1644.429266','SA_REP',8800.00,0.25,149,80,'2014-03-05 00:00:00'),(176,'Jonathon','Taylor','JTAYLOR','011.44.1644.429265','SA_REP',8600.00,0.20,149,80,'2014-03-05 00:00:00'),(177,'Jack','Livingston','JLIVINGS','011.44.1644.429264','SA_REP',8400.00,0.20,149,80,'2014-03-05 00:00:00'),(178,'Kimberely','Grant','KGRANT','011.44.1644.429263','SA_REP',7000.00,0.15,149,NULL,'2014-03-05 00:00:00'),(179,'Charles','Johnson','CJOHNSON','011.44.1644.429262','SA_REP',6200.00,0.10,149,80,'2014-03-05 00:00:00'),(180,'Winston','Taylor','WTAYLOR','650.507.9876','SH_CLERK',3200.00,NULL,120,50,'2014-03-05 00:00:00'),(181,'Jean','Fleaur','JFLEAUR','650.507.9877','SH_CLERK',3100.00,NULL,120,50,'2014-03-05 00:00:00'),(182,'Martha','Sullivan','MSULLIVA','650.507.9878','SH_CLERK',2500.00,NULL,120,50,'2014-03-05 00:00:00'),(183,'Girard','Geoni','GGEONI','650.507.9879','SH_CLERK',2800.00,NULL,120,50,'2014-03-05 00:00:00'),(184,'Nandita','Sarchand','NSARCHAN','650.509.1876','SH_CLERK',4200.00,NULL,121,50,'2014-03-05 00:00:00'),(185,'Alexis','Bull','ABULL','650.509.2876','SH_CLERK',4100.00,NULL,121,50,'2014-03-05 00:00:00'),(186,'Julia','Dellinger','JDELLING','650.509.3876','SH_CLERK',3400.00,NULL,121,50,'2014-03-05 00:00:00'),(187,'Anthony','Cabrio','ACABRIO','650.509.4876','SH_CLERK',3000.00,NULL,121,50,'2014-03-05 00:00:00'),(188,'Kelly','Chung','KCHUNG','650.505.1876','SH_CLERK',3800.00,NULL,122,50,'2014-03-05 00:00:00'),(189,'Jennifer','Dilly','JDILLY','650.505.2876','SH_CLERK',3600.00,NULL,122,50,'2014-03-05 00:00:00'),(190,'Timothy','Gates','TGATES','650.505.3876','SH_CLERK',2900.00,NULL,122,50,'2014-03-05 00:00:00'),(191,'Randall','Perkins','RPERKINS','650.505.4876','SH_CLERK',2500.00,NULL,122,50,'2014-03-05 00:00:00'),(192,'Sarah','Bell','SBELL','650.501.1876','SH_CLERK',4000.00,NULL,123,50,'2014-03-05 00:00:00'),(193,'Britney','Everett','BEVERETT','650.501.2876','SH_CLERK',3900.00,NULL,123,50,'2014-03-05 00:00:00'),(194,'Samuel','McCain','SMCCAIN','650.501.3876','SH_CLERK',3200.00,NULL,123,50,'2014-03-05 00:00:00'),(195,'Vance','Jones','VJONES','650.501.4876','SH_CLERK',2800.00,NULL,123,50,'2014-03-05 00:00:00'),(196,'Alana','Walsh','AWALSH','650.507.9811','SH_CLERK',3100.00,NULL,124,50,'2014-03-05 00:00:00'),(197,'Kevin','Feeney','KFEENEY','650.507.9822','SH_CLERK',3000.00,NULL,124,50,'2014-03-05 00:00:00'),(198,'Donald','OConnell','DOCONNEL','650.507.9833','SH_CLERK',2600.00,NULL,124,50,'2014-03-05 00:00:00'),(199,'Douglas','Grant','DGRANT','650.507.9844','SH_CLERK',2600.00,NULL,124,50,'2014-03-05 00:00:00'),(200,'Jennifer','Whalen','JWHALEN','515.123.4444','AD_ASST',4400.00,NULL,101,10,'2016-03-03 00:00:00'),(201,'Michael','Hartstein','MHARTSTE','515.123.5555','MK_MAN',13000.00,NULL,100,20,'2016-03-03 00:00:00'),(202,'Pat','Fay','PFAY','603.123.6666','MK_REP',6000.00,NULL,201,20,'2016-03-03 00:00:00'),(203,'Susan','Mavris','SMAVRIS','515.123.7777','HR_REP',6500.00,NULL,101,40,'2016-03-03 00:00:00'),(204,'Hermann','Baer','HBAER','515.123.8888','PR_REP',10000.00,NULL,101,70,'2016-03-03 00:00:00'),(205,'Shelley','Higgins','SHIGGINS','515.123.8080','AC_MGR',12000.00,NULL,101,110,'2016-03-03 00:00:00'),(206,'William','Gietz','WGIETZ','515.123.8181','AC_ACCOUNT',8300.00,NULL,205,110,'2016-03-03 00:00:00');
/*职位信息表*/
DROP TABLE IF EXISTS `jobs`;
CREATE TABLE `jobs` (
`job_id` varchar(10) NOT NULL comment '职位id',
`job_title` varchar(35) DEFAULT NULL comment '职位名称',
`min_salary` int(6) DEFAULT NULL comment '薪资范围最小值',
`max_salary` int(6) DEFAULT NULL comment '薪资范围最大值',
PRIMARY KEY (`job_id`)
) ENGINE=InnoDB comment '职位id';
insert into `jobs`(`job_id`,`job_title`,`min_salary`,`max_salary`) values ('AC_ACCOUNT','Public Accountant',4200,9000),('AC_MGR','Accounting Manager',8200,16000),('AD_ASST','Administration Assistant',3000,6000),('AD_PRES','President',20000,40000),('AD_VP','Administration Vice President',15000,30000),('FI_ACCOUNT','Accountant',4200,9000),('FI_MGR','Finance Manager',8200,16000),('HR_REP','Human Resources Representative',4000,9000),('IT_PROG','Programmer',4000,10000),('MK_MAN','Marketing Manager',9000,15000),('MK_REP','Marketing Representative',4000,9000),('PR_REP','Public Relations Representative',4500,10500),('PU_CLERK','Purchasing Clerk',2500,5500),('PU_MAN','Purchasing Manager',8000,15000),('SA_MAN','Sales Manager',10000,20000),('SA_REP','Sales Representative',6000,12000),('SH_CLERK','Shipping Clerk',2500,5500),('ST_CLERK','Stock Clerk',2000,5000),('ST_MAN','Stock Manager',5500,8500);
/*位置表*/
DROP TABLE IF EXISTS `locations`;
CREATE TABLE `locations` (
`location_id` int(11) NOT NULL AUTO_INCREMENT comment '位置id',
`street_address` varchar(40) DEFAULT NULL comment '街道地址',
`postal_code` varchar(12) DEFAULT NULL comment '邮编',
`city` varchar(30) DEFAULT NULL comment '城市名称',
`state_province` varchar(25) DEFAULT NULL comment '省',
`country_id` varchar(2) DEFAULT NULL comment '国家编号',
PRIMARY KEY (`location_id`)
) ENGINE=InnoDB AUTO_INCREMENT=3201 comment '位置表';
insert into `locations`(`location_id`,`street_address`,`postal_code`,`city`,`state_province`,`country_id`) values (1000,'1297 Via Cola di Rie','00989','Roma',NULL,'IT'),(1100,'93091 Calle della Testa','10934','Venice',NULL,'IT'),(1200,'2017 Shinjuku-ku','1689','Tokyo','Tokyo Prefecture','JP'),(1300,'9450 Kamiya-cho','6823','Hiroshima',NULL,'JP'),(1400,'2014 Jabberwocky Rd','26192','Southlake','Texas','US'),(1500,'2011 Interiors Blvd','99236','South San Francisco','California','US'),(1600,'2007 Zagora St','50090','South Brunswick','New Jersey','US'),(1700,'2004 Charade Rd','98199','Seattle','Washington','US'),(1800,'147 Spadina Ave','M5V 2L7','Toronto','Ontario','CA'),(1900,'6092 Boxwood St','YSW 9T2','Whitehorse','Yukon','CA'),(2000,'40-5-12 Laogianggen','190518','Beijing',NULL,'CN'),(2100,'1298 Vileparle (E)','490231','Bombay','Maharashtra','IN'),(2200,'12-98 Victoria Street','2901','Sydney','New South Wales','AU'),(2300,'198 Clementi North','540198','Singapore',NULL,'SG'),(2400,'8204 Arthur St',NULL,'London',NULL,'UK'),(2500,'Magdalen Centre, The Oxford Science Park','OX9 9ZB','Oxford','Oxford','UK'),(2600,'9702 Chester Road','09629850293','Stretford','Manchester','UK'),(2700,'Schwanthalerstr. 7031','80925','Munich','Bavaria','DE'),(2800,'Rua Frei Caneca 1360 ','01307-002','Sao Paulo','Sao Paulo','BR'),(2900,'20 Rue des Corps-Saints','1730','Geneva','Geneve','CH'),(3000,'Murtenstrasse 921','3095','Bern','BE','CH'),(3100,'Pieter Breughelstraat 837','3029SK','Utrecht','Utrecht','NL'),(3200,'Mariano Escobedo 9991','11932','Mexico City','Distrito Federal,','MX');
/*薪资等级表*/
DROP TABLE IF EXISTS `job_grades`;
CREATE TABLE `job_grades`(
`grade_level` varchar(3) comment '等级',
`lowest_sal` int comment '薪资最低值',
`highest_sal` int comment '薪资最高值',
PRIMARY KEY (`grade_level`)
) comment '薪资等级表';
INSERT INTO job_grades VALUES ('A', 1000, 2999),('B', 3000, 5999),('C', 6000, 9999),('D', 10000, 14999),('E', 15000, 24999),('F', 25000, 40000);
employees 库及5张表，如下：
| 表名 | 描述 |
|---|---|
| departments | 部门表 |
| employees | 员工信息表 |
| jobs | 职位信息表 |
| locations | 位置表（部门表中会用到） |
| job_grades | 薪资等级表 |
创建视图
语法
create view 视图名
as
查询语句;
创建视图的使用步骤
- 创建视图
- 对视图执行查询操作
案例1
查询姓名中包含a字段的员工名、部门、工种信息
/*案例1：查询姓名中包含a字符的员工名、部门、工种信息*/
/*创建视图*/
CREATE VIEW myview1
AS
SELECT
t1.last_name,
t2.department_name,
t3.job_title
FROM employees t1,departments t2,jobs t3
WHERE t1.department_id = t2.department_id
AND t1.job_id = t3.job_id;
/*使用视图*/
mysql> select * from myview1 where last_name like 'a%';
+-----------+-----------------+----------------------+
| last_name | department_name | job_title |
+-----------+-----------------+----------------------+
| Austin | IT | Programmer |
| Atkinson | Shi | Stock Clerk |
| Ande | Sal | Sales Representative |
| Abel | Sal | Sales Representative |
+-----------+-----------------+----------------------+
4 rows in set (0.00 sec)
上面我们创建了一个视图： myv1 ，我们需要看 员工姓名、部门、工种 信息的时候，不用关心这个视图内部是什么样的，只需要查询视图就可以了，sql简单多了。
案例2
案例2：查询各部门的平均工资级别
/*案例2：查询各部门的平均工资级别*/
/*创建视图myview2*/
CREATE VIEW myview2
AS
SELECT
t1.department_id 部门id,
t1.ag 平均工资,
t2.grade_level 工资级别
FROM (SELECT
department_id,
AVG(salary) ag
FROM employees
GROUP BY department_id) t1, job_grades t2
WHERE t1.ag BETWEEN t2.lowest_sal AND t2.highest_sal;
/*使用视图*/
mysql> select * from myview2;
+----------+--------------+--------------+
| 部门id | 平均工资 | 工资级别 |
+----------+--------------+--------------+
| NULL | 7000.000000 | C |
| 10 | 4400.000000 | B |
| 20 | 9500.000000 | C |
| 30 | 4150.000000 | B |
| 40 | 6500.000000 | C |
| 50 | 3475.555556 | B |
| 60 | 5760.000000 | B |
| 70 | 10000.000000 | D |
| 80 | 8955.882353 | C |
| 90 | 19333.333333 | E |
| 100 | 8600.000000 | C |
| 110 | 10150.000000 | D |
+----------+--------------+--------------+
12 rows in set (0.00 sec)
修改视图
两种方式
方式1
如果存在视图，就修改，如果不存在就创建新的视图
create or replace view 视图名
as
查询语句;
示例
CREATE OR REPLACE VIEW myview3
AS
SELECT
job_id,
AVG(salary) jid_avg
FROM employees
GROUP BY job_id
mysql> select * from myview3;
+------------+--------------+
| job_id | jid_avg |
+------------+--------------+
| AC_ACCOUNT | 8300.000000 |
| AC_MGR | 12000.000000 |
| AD_ASST | 4400.000000 |
| AD_PRES | 24000.000000 |
| AD_VP | 17000.000000 |
| FI_ACCOUNT | 7920.000000 |
| FI_MGR | 12000.000000 |
| HR_REP | 6500.000000 |
| IT_PROG | 5760.000000 |
| MK_MAN | 13000.000000 |
| MK_REP | 6000.000000 |
| PR_REP | 10000.000000 |
| PU_CLERK | 2780.000000 |
| PU_MAN | 11000.000000 |
| SA_MAN | 12200.000000 |
| SA_REP | 8350.000000 |
| SH_CLERK | 3215.000000 |
| ST_CLERK | 2785.000000 |
| ST_MAN | 7280.000000 |
+------------+--------------+
19 rows in set (0.00 sec)
方式2
alter view 视图名
as
查询语句;
示例
mysql> select * from myview3 limit 1\G
*************************** 1. row ***************************
employee_id: 100
first_name: Steven
last_name: K_ing
email: SKING
phone_number: 515.123.4567
job_id: AD_PRES
salary: 24000.00
commission_pct: NULL
manager_id: NULL
department_id: 90
hiredate: 1992-04-03 00:00:00
1 rows in set (0.00 sec)
删除视图
语法
drop view 视图名1 [,视图名2] [,视图名n];
可以同时删除多个视图，多个视图名称之间用逗号隔开
示例
mysql> drop view myview1,myview2,myview3;
Query OK, 0 rows affected (0.01 sec)
查询视图结构
- desc 视图名称；
- show create view 视图名称；
- show table status
- select * from information_schema.views
方法1
desc 视图名称
例子：
mysql> desc myview1;
+-----------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+-------------+------+-----+---------+-------+
| last_name | varchar(25) | YES | | NULL | |
| department_name | varchar(3) | YES | | NULL | |
| job_title | varchar(35) | YES | | NULL | |
+-----------------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
方法2
show create view 视图名称;
例子：
mysql> show create view myview1\G
*************************** 1. row ***************************
View: myview1
Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `myview1` AS select `t1`.`last_name` AS `last_name`,`t2`.`department_name` AS `department_name`,`t3`.`job_title` AS `job_title` from ((`employees` `t1` join `departments` `t2`) join `jobs` `t3`) where ((`t1`.`department_id` = `t2`.`department_id`) and (`t1`.`job_id` = `t3`.`job_id`))
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
1 row in set (0.00 sec)
方法3
show table status like 'view_name'
示例
mysql> SHOW TABLE STATUS LIKE 'myview1'\G
*************************** 1. row ***************************
Name: myview1
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)
Comment 属性的值为 VIEW，说明 myview1为视图，其他信息为 NULL，说明视图是一张虚拟表。
方法4
查看views表
MySQL 中会将视图的信息存储到 information_schema 数据库下的 views 数据表中，可以查看 views 数据表来查看视图的信息。
SELECT * FROM information_schema.views \G
示例
mysql> SELECT * FROM information_schema.views where table_name = 'myview1'\G
*************************** 1. row ***************************
TABLE_CATALOG: def
TABLE_SCHEMA: employees
TABLE_NAME: myview1
VIEW_DEFINITION: select `t1`.`last_name` AS `last_name`,`t2`.`department_name` AS `department_name`,`t3`.`job_title` AS `job_title` from `employees`.`employees` `t1` join `employees`.`departments` `t2` join `employees`.`jobs` `t3` where ((`t1`.`department_id` = `t2`.`department_id`) and (`t1`.`job_id` = `t3`.`job_id`))
CHECK_OPTION: NONE
IS_UPDATABLE: YES
DEFINER: root@localhost
SECURITY_TYPE: DEFINER
CHARACTER_SET_CLIENT: utf8mb4
COLLATION_CONNECTION: utf8mb4_general_ci
1 row in set (0.00 sec)
更新视图（尽量不用）
更新视图是指通过视图，来更新、插入、删除基本表中的数据。视图是一个虚拟表，即对视图的更新，实质上是更新基表。
也就是说：视图的更新是更改视图中的数据，而不是更改视图中的sql逻辑。当对视图进行更新后，也会对原始表的数据进行更新。
但是视图的构造很多时候是由多个表连接查询，以及结合聚合函数，分组过滤等等定义的。对于这类的视图，想要去更新，恐怕就显得力不从心了，更何况通过更改视图来修改数据，会造成混乱，不易管理。
为了防止对原始表的数据产生更新，可以为视图添加只读权限，只允许读视图，不允许对视图进行更新。
所以，一般尽量不使用视图的更新操作
示例：
CREATE VIEW myview4
AS
SELECT last_name,email from employees;
-- 插入
mysql> insert into myview4 VALUES ('周星驰','123456789@163.com');
Query OK, 1 row affected (0.00 sec)
mysql> select * from myview4 where email like '123456789%';
+-----------+-------------------+
| last_name | email |
+-----------+-------------------+
| 周星驰 | 123456789@163.com |
+-----------+-------------------+
1 row in set (0.00 sec)
mysql> select last_name,email from employees where email like '123456789%';
+-----------+-------------------+
| last_name | email |
+-----------+-------------------+
| 周星驰 | 123456789@163.com |
+-----------+-------------------+
1 row in set (0.00 sec)
#更改了原表数据，所以视图更新尽量不用，了解即可
-- 修改
update myview4 set last_name = '张国荣' where last_name = '周星驰';
mysql> select * from myview4 where last_name like '张国荣';
+-----------+-------------------+
| last_name | email |
+-----------+-------------------+
| 张国荣 | 123456789@163.com |
+-----------+-------------------+
1 row in set (0.00 sec)
-- 删除
delete from myview4 where last_name = '张国荣';
mysql> select * from myview4 where email like '123456789%';
Empty set (0.00 sec)
