#视图
/*
含义:虚拟表,和普通表一样使用,mysql5.0.1版本开始的特性
行和列的数据来自定义视图的查询中使用的表,并且是在使用视图时动态生成的,只保存sql逻辑,不保存查询结果。
应用场景:
-多个地方用到同样的查询结果
-该查询结果使用的sql语句较复杂
特点:
1.重用sql语句
2.简化复杂的sql操作
3.保护数据,提高安全性
创建语法的关键字 是否实际占用物理空间 使用
视图 create view 只是保存了sql逻辑 增删改查,只是一般不能增删改
表 create table 保存了数据 增删改查
*/
#案例1:查询job_id为AD_VP的员工名和job_title
USE myemployees;
SELECT last_name,job_title,salary
FROM employees e
INNER JOIN jobs j ON e.`job_id`=j.`job_id`
WHERE e.`job_id`='AD_VP';
##用视图方式完成
CREATE VIEW temp1
AS
SELECT last_name,job_title,salary
FROM employees e
INNER JOIN jobs j ON e.`job_id`=j.`job_id`
WHERE e.`job_id`='AD_VP';
SELECT * FROM temp1;
#一、创建视图
/*
语法:
create view 视图名
as
查询语句;
*/
#1.查询姓名中包含a字符的员工名、部门名和工种信息
##创建视图
CREATE VIEW myv1
AS
SELECT last_name,department_name,job_title
FROM employees e
INNER JOIN departments d ON e.department_id=d.department_id
INNER JOIN jobs j ON e.job_id=j.job_id;
##选择筛选
SELECT * FROM myv1 WHERE last_name LIKE '%a%';
#2.查询各部门的平均工资级别
##创建各部门平均工资视图
CREATE VIEW myv2
AS
SELECT AVG(salary) ag,department_id
FROM employees e
GROUP BY e.department_id;
##非等值连接
SELECT myv2.*,g.`grade_level`
FROM myv2
INNER JOIN job_grades g
ON myv2.ag BETWEEN g.`lowest_sal` AND g.`highest_sal`;
#3.查询平均工资最低的部门id
SELECT * FROM myv2 ORDER BY ag LIMIT 1;
#4.查询平均工资最低的部门名和工资
SELECT department_name,myv2.ag
FROM myv2
JOIN departments d
ON myv2.`department_id`=d.`department_id`
ORDER BY ag
LIMIT 1;
#二、视图的修改
/*
方式一:
语法:
create or replace view 视图名
as
查询语句;
###存在则修改,不存在则创建
方式二:
语法:
alter view 视图名
as
查询语句;
*/
SELECT * FROM myv3;
#方式一
CREATE OR REPLACE VIEW myv3
AS
SELECT AVG(salary) ag,job_id
FROM employees
GROUP BY job_id;
#方式二
ALTER VIEW myv3
AS
SELECT * FROM employees;
#三、删除视图
/*
语法:(可多个一次删除)
drop view 视图名,视图名,……;
*/
DROP VIEW temp1;
#四、查看视图
/*
desc 视图名
show create view 视图名
*/
DESC temp1;
SHOW CREATE VIEW myv3;
#=======================Test=================
#1、创建视图emp_v1,要求查询电话号码以‘011’开头的员工姓名和工资、邮箱
##1
CREATE OR REPLACE VIEW emp_v1
AS
SELECT last_name,salary,email,phone_number
FROM employees
WHERE phone_number LIKE '011%';
SELECT * FROM emp_v1;
#2、创建视图emp_v2,要求查询部门的最高工资高于12000的部门信息
USE myemployees;
##1部门最高工资
CREATE OR REPLACE VIEW emp_v2
AS
SELECT MAX(salary) maxsa,department_name
FROM employees e
JOIN departments d ON e.`department_id`=d.`department_id`
GROUP BY e.department_id;
##2选高于12000的信息
SELECT emp_v2.maxsa,d.*
FROM emp_v2
JOIN departments d ON emp_v2.`department_name`=d.`department_name`
WHERE emp_v2.maxsa>12000;
#===========================end Test==========================
#五、视图的更新
DROP VIEW myv1,myv2,myv3;
CREATE OR REPLACE VIEW myv1
AS
SELECT last_name,email,salary*12*(1+IFNULL(commission_pct,0)) "annual salary"
FROM employees;
CREATE OR REPLACE VIEW myv1
AS
SELECT last_name,email
FROM employees;
SELECT * FROM myv1;
SELECT * FROM employees;
#视图的更新会造成视图和原表一起更新。若原表没有此字段数据,则可能无法更新
#1.插入
INSERT INTO myv1 VALUE("张飞","zhangfei1");
#2.修改
UPDATE myv1 SET last_name="张无忌" WHERE last_name="张飞";
#3.删除
DELETE FROM myv1 WHERE last_name="张无忌";
#具备以下特点的视图不允许更新:
/*
1.包含以下关键字的sql语句:
分组函数、distinct、group by、having、union或者union all
2.常量视图(视图数据是一个常量)
3.Select中包含子查询
4.join连接查询
5.from一个不能更新的视图的视图
6.where子句的子查询引用了from子句中的表
*/
/*
含义:虚拟表,和普通表一样使用,mysql5.0.1版本开始的特性
行和列的数据来自定义视图的查询中使用的表,并且是在使用视图时动态生成的,只保存sql逻辑,不保存查询结果。
应用场景:
-多个地方用到同样的查询结果
-该查询结果使用的sql语句较复杂
特点:
1.重用sql语句
2.简化复杂的sql操作
3.保护数据,提高安全性
创建语法的关键字 是否实际占用物理空间 使用
视图 create view 只是保存了sql逻辑 增删改查,只是一般不能增删改
表 create table 保存了数据 增删改查
*/
#案例1:查询job_id为AD_VP的员工名和job_title
USE myemployees;
SELECT last_name,job_title,salary
FROM employees e
INNER JOIN jobs j ON e.`job_id`=j.`job_id`
WHERE e.`job_id`='AD_VP';
##用视图方式完成
CREATE VIEW temp1
AS
SELECT last_name,job_title,salary
FROM employees e
INNER JOIN jobs j ON e.`job_id`=j.`job_id`
WHERE e.`job_id`='AD_VP';
SELECT * FROM temp1;
#一、创建视图
/*
语法:
create view 视图名
as
查询语句;
*/
#1.查询姓名中包含a字符的员工名、部门名和工种信息
##创建视图
CREATE VIEW myv1
AS
SELECT last_name,department_name,job_title
FROM employees e
INNER JOIN departments d ON e.department_id=d.department_id
INNER JOIN jobs j ON e.job_id=j.job_id;
##选择筛选
SELECT * FROM myv1 WHERE last_name LIKE '%a%';
#2.查询各部门的平均工资级别
##创建各部门平均工资视图
CREATE VIEW myv2
AS
SELECT AVG(salary) ag,department_id
FROM employees e
GROUP BY e.department_id;
##非等值连接
SELECT myv2.*,g.`grade_level`
FROM myv2
INNER JOIN job_grades g
ON myv2.ag BETWEEN g.`lowest_sal` AND g.`highest_sal`;
#3.查询平均工资最低的部门id
SELECT * FROM myv2 ORDER BY ag LIMIT 1;
#4.查询平均工资最低的部门名和工资
SELECT department_name,myv2.ag
FROM myv2
JOIN departments d
ON myv2.`department_id`=d.`department_id`
ORDER BY ag
LIMIT 1;
#二、视图的修改
/*
方式一:
语法:
create or replace view 视图名
as
查询语句;
###存在则修改,不存在则创建
方式二:
语法:
alter view 视图名
as
查询语句;
*/
SELECT * FROM myv3;
#方式一
CREATE OR REPLACE VIEW myv3
AS
SELECT AVG(salary) ag,job_id
FROM employees
GROUP BY job_id;
#方式二
ALTER VIEW myv3
AS
SELECT * FROM employees;
#三、删除视图
/*
语法:(可多个一次删除)
drop view 视图名,视图名,……;
*/
DROP VIEW temp1;
#四、查看视图
/*
desc 视图名
show create view 视图名
*/
DESC temp1;
SHOW CREATE VIEW myv3;
#=======================Test=================
#1、创建视图emp_v1,要求查询电话号码以‘011’开头的员工姓名和工资、邮箱
##1
CREATE OR REPLACE VIEW emp_v1
AS
SELECT last_name,salary,email,phone_number
FROM employees
WHERE phone_number LIKE '011%';
SELECT * FROM emp_v1;
#2、创建视图emp_v2,要求查询部门的最高工资高于12000的部门信息
USE myemployees;
##1部门最高工资
CREATE OR REPLACE VIEW emp_v2
AS
SELECT MAX(salary) maxsa,department_name
FROM employees e
JOIN departments d ON e.`department_id`=d.`department_id`
GROUP BY e.department_id;
##2选高于12000的信息
SELECT emp_v2.maxsa,d.*
FROM emp_v2
JOIN departments d ON emp_v2.`department_name`=d.`department_name`
WHERE emp_v2.maxsa>12000;
#===========================end Test==========================
#五、视图的更新
DROP VIEW myv1,myv2,myv3;
CREATE OR REPLACE VIEW myv1
AS
SELECT last_name,email,salary*12*(1+IFNULL(commission_pct,0)) "annual salary"
FROM employees;
CREATE OR REPLACE VIEW myv1
AS
SELECT last_name,email
FROM employees;
SELECT * FROM myv1;
SELECT * FROM employees;
#视图的更新会造成视图和原表一起更新。若原表没有此字段数据,则可能无法更新
#1.插入
INSERT INTO myv1 VALUE("张飞","zhangfei1");
#2.修改
UPDATE myv1 SET last_name="张无忌" WHERE last_name="张飞";
#3.删除
DELETE FROM myv1 WHERE last_name="张无忌";
#具备以下特点的视图不允许更新:
/*
1.包含以下关键字的sql语句:
分组函数、distinct、group by、having、union或者union all
2.常量视图(视图数据是一个常量)
3.Select中包含子查询
4.join连接查询
5.from一个不能更新的视图的视图
6.where子句的子查询引用了from子句中的表
*/