MySQL-其他

#视图

/*

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

比如：舞蹈班和普通班级的对比

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：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

AS

SELECT 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：

/*

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,...;

*/

DROP VIEW emp_v1,emp_v2,myv3;

#四、查看视图

DESC myv3;

SHOW CREATE VIEW myv3;

#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

#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

CREATE 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

AS

SELECT ‘john‘ NAME;

SELECT * FROM myv2;

#更新

UPDATE myv2 SET NAME=‘lucy‘;

#③Select中包含子查询

CREATE OR REPLACE VIEW myv3

AS

SELECT 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

AS

SELECT 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

AS

SELECT * 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

AS

SELECT last_name,email,salary

FROM employees

WHERE employee_id IN(

SELECT  manager_id

FROM employees

WHERE manager_id IS NOT NULL

);

#更新

SELECT * FROM myv6;

UPDATE myv6 SET salary=10000 WHERE last_name = ‘k_ing‘;

#练习

#一、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

CREATE OR REPLACE VIEW emp_v1

AS

SELECT last_name,salary,email

FROM employees

WHERE phone_number LIKE ‘011%‘;

#二、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

CREATE OR REPLACE VIEW emp_v2

AS

SELECT MAX(salary) mx_dep,department_id

FROM employees

GROUP BY department_id

HAVING MAX(salary)>12000;

SELECT d.*,m.mx_dep

FROM departments d

JOIN emp_v2 m

ON m.department_id = d.`department_id`;

#标识列

/*

又称为自增长列

含义：可以不用手动的插入值，系统提供默认的序列值

特点：

1、标识列必须和主键搭配吗？不一定，但要求是一个key

2、一个表可以有几个标识列？至多一个！

3、标识列的类型只能是数值型

4、标识列可以通过SET auto_increment_increment=3;设置步长

可以通过 手动插入值，设置起始值

*/

#一、创建表时设置标识列

DROP TABLE IF EXISTS tab_identity;

CREATE TABLE tab_identity(

id INT  ,

NAME FLOAT UNIQUE AUTO_INCREMENT,

seat INT

);

TRUNCATE TABLE tab_identity;

INSERT INTO tab_identity(id,NAME) VALUES(NULL,‘john‘);

INSERT INTO tab_identity(NAME) VALUES(‘lucy‘);

SELECT * FROM tab_identity;

SHOW VARIABLES LIKE ‘%auto_increment%‘;

SET auto_increment_increment=3;

原文：https://www.cnblogs.com/LXL616/p/10841276.html