视图
含义:理解成一张虚拟的表,和普通表一样使用
mysql5.1版本出现的新特性,是通过表动态生成的数据
比如:舞蹈班和普通班级的对比
视图和表的区别:
名称 | 创建语法的关键字 | 使用 | 占用物理空间 |
---|---|---|---|
视图 | create view | 增删改查,只是一般不能增删改 | 不占用,仅仅保存的是sql逻辑 |
表 | create table | 增删改查 | 占用 |
视图的好处:
1、sql语句提高重用性,效率高
2、和表实现了分离,提高了安全性
视图的创建
语法:
CREATE VIEW 视图名
AS
查询语句;
视图的增删改查
1、查看视图的数据 ★SELECT * FROM my_v4;
SELECT * FROM my_v1 WHERE last_name='Partners';2、插入视图的数据
INSERT INTO my_v4(last_name,department_id) VALUES('虚竹',90);3、修改视图的数据UPDATE my_v4 SET last_name ='梦姑' WHERE last_name='虚竹';4、删除视图的数据
DELETE FROM my_v4;
某些视图不能更新
包含以下关键字的sql语句:分组函数、distinct、group by、having、union或者union all
常量视图
Select中包含子查询
join
from一个不能更新的视图
where子句的子查询引用了from子句中的表
视图逻辑的更新
#方式一:
CREATE OR REPLACE VIEW test_v7
AS
SELECT last_name FROM employees
WHERE employee_id>100;方式二:
ALTER VIEW test_v7
AS
SELECT employee_id FROM employees;SELECT * FROM test_v7;
视图的删除
DROP VIEW test_v1,test_v2,test_v3;
视图结构的查看
DESC test_v7;
SHOW CREATE VIEW test_v7;
一、创建视图
语法:
create view 视图名
as
查询语句;
#案例:查询姓张的学生名和专业名
SELECT stuname,majorname
FROM stuinfo s
INNER JOIN major m ON s.`majorid`= m.`id`
WHERE s.`stuname` LIKE '张%';CREATE VIEW v1
AS
SELECT stuname,majorname
FROM stuinfo s
INNER JOIN major m ON s.`majorid`= m.`id`;SELECT * FROM v1 WHERE stuname LIKE '张%';#一、创建视图
/*
语法:
create view 视图名
as
查询语句;*/
USE myemployees;#1.查询姓名中包含a字符的员工名、部门名和工种信息
#①创建
CREATE VIEW myv1
ASSELECT last_name,department_name,job_title
FROM employees e
JOIN departments d ON e.department_id = d.department_id
JOIN jobs j ON j.job_id = e.job_id;#②使用
SELECT * FROM myv1 WHERE last_name LIKE '%a%';#2.查询各部门的平均工资级别#①创建视图查看每个部门的平均工资
CREATE VIEW myv2
AS
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id;#②使用
SELECT myv2.`ag`,g.grade_level
FROM myv2
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信息SELECT * FROM myv2 ORDER BY ag LIMIT 1;#4.查询平均工资最低的部门名和工资CREATE VIEW myv3
AS
SELECT * FROM myv2 ORDER BY ag LIMIT 1;SELECT d.*,m.ag
FROM myv3 m
JOIN departments d
ON m.`department_id`=d.`department_id`;
二、视图的修改
方式一:
语法:
create or replace view 视图名
as
查询语句;
方式二:
语法:
alter view 视图名
as
查询语句;
#二、视图的修改#方式一:
/*
create or replace view 视图名
as
查询语句;*/
SELECT * FROM myv3 CREATE OR REPLACE VIEW myv3
AS
SELECT AVG(salary),job_id
FROM employees
GROUP BY job_id;#方式二:
/*
语法:
alter view 视图名
as
查询语句;*/
ALTER VIEW myv3
AS
SELECT * FROM employees;
三、删除视图
语法:drop view 视图名,视图名,…;
#三、删除视图/*语法:drop view 视图名,视图名,...;
*/DROP VIEW emp_v1,emp_v2,myv3;
四、查看视图
#四、查看视图DESC myv3;SHOW CREATE VIEW myv3;
五、视图的更新
#五、视图的更新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;
#1.插入INSERT INTO myv1 VALUES('张飞','zf@qq.com');#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 allCREATE OR REPLACE VIEW myv1
AS
SELECT MAX(salary) m,department_id
FROM employees
GROUP BY department_id;SELECT * FROM myv1;#更新
UPDATE myv1 SET m=9000 WHERE department_id=10;#②常量视图
CREATE OR REPLACE VIEW myv2
ASSELECT 'john' NAME;SELECT * FROM myv2;#更新
UPDATE myv2 SET NAME='lucy';#③Select中包含子查询CREATE OR REPLACE VIEW myv3
ASSELECT department_id,(SELECT MAX(salary) FROM employees) 最高工资
FROM departments;#更新
SELECT * FROM myv3;
UPDATE myv3 SET 最高工资=100000;#④join
CREATE OR REPLACE VIEW myv4
ASSELECT last_name,department_name
FROM employees e
JOIN departments d
ON e.department_id = d.department_id;#更新SELECT * FROM myv4;
UPDATE myv4 SET last_name = '张飞' WHERE last_name='Whalen';
INSERT INTO myv4 VALUES('陈真','xxxx');#⑤from一个不能更新的视图
CREATE OR REPLACE VIEW myv5
ASSELECT * FROM myv3;#更新SELECT * FROM myv5;UPDATE myv5 SET 最高工资=10000 WHERE department_id=60;#⑥where子句的子查询引用了from子句中的表CREATE OR REPLACE VIEW myv6
ASSELECT last_name,email,salary
FROM employees
WHERE employee_id IN(SELECT manager_idFROM employeesWHERE manager_id IS NOT NULL
);#更新
SELECT * FROM myv6;
UPDATE myv6 SET salary=10000 WHERE last_name = 'k_ing';