MySQL之视图(MySQL第五课)
作者:互联网
基础知识:
含义:虚拟表,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
比较:
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:查询姓张的学生名和专业名
连表查询:
SELECT stuname,majorname
FROM stuinfo s
INNER JOIN major m ON s.`majorid`= m.`id`
WHERE s.`stuname` LIKE '张%';
使用视图:
CREATE VIEW v1
AS
SELECT stuname,majorname
FROM stuinfo s
INNER JOIN major m ON s.`majorid`= m.`id`;
最终结果:SELECT * FROM v1 WHERE stuname LIKE '张%';
一、创建视图
语法:create view 视图名 as 查询语句;
-- 创建视图
-- 查询姓名中包含a字符的员工名、部门名和工种信息
CREATE VIEW lgs1
AS
SELECT last_name,department_name,job_title
FROM t_mysql_employees e
JOIN t_mysql_departments d ON e.department_id = d.department_id
JOIN t_mysql_jobs j ON j.job_id = e.job_id;
-- 使用
select * from lgs1 WHERE last_name LIKE '%a%';
二、视图的修改
方式一:create or replace view 视图名 as 查询语句;
-- 修改为查询员工名和最大工资
CREATE OR REPLACE VIEW lgs1
AS
SELECT AVG(max_salary),job_id
FROM t_mysql_jobs
GROUP BY job_id;
select * from lgs1
方式二:alter view 视图名 as 查询语句;
-- 修改为查询t_mysql_employees表信息
ALTER VIEW lgs1
AS
SELECT * FROM t_mysql_employees;
select * from lgs1
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
DESC myv3;
SHOW CREATE VIEW myv3;
五、视图的更新
-- 更新前
CREATE OR REPLACE VIEW lgs1
AS
SELECT last_name,email,salary*12*(1+IFNULL(commission_pct,0)) "annual salary"
FROM t_mysql_employees;
-- 更新后
CREATE OR REPLACE VIEW myv1
AS
SELECT last_name,email
FROM t_mysql_employees;
视图操作:
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 all
2,常量视图
3,Select中包含子查询
4,join
5,from一个不能更新的视图
6,where子句的子查询引用了from子句中的表
标签:name,MySQL,第五课,视图,mysql,id,SELECT,VIEW 来源: https://blog.csdn.net/m0_58525944/article/details/120206633