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/*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,majornameFROM stuinfo sINNER JOIN major m ON s.`majorid`= m.`id`WHERE s.`stuname` LIKE '张%';
创建视图
CREATE VIEW v1ASSELECT stuname,majornameFROM stuinfo sINNER JOIN major m ON s.`majorid`= m.`id`;
查询姓张的学生名和专业名 (视图方式)
SELECT * FROM v1 WHERE stuname LIKE '张%';
/*语法:create view 视图名as查询语句;*/USE myemployees;
#①创建CREATE VIEW myv1ASSELECT last_name,department_name,job_titleFROM employees eJOIN departments d ON e.department_id = d.department_idJOIN jobs j ON j.job_id = e.job_id;#②使用SELECT * FROM myv1 WHERE last_name LIKE '%a%';
#①创建视图查看每个部门的平均工资CREATE VIEW myv2ASSELECT AVG(salary) ag,department_idFROM employeesGROUP BY department_id;#②使用SELECT myv2.`ag`,g.grade_levelFROM myv2JOIN job_grades gON myv2.`ag` BETWEEN g.`lowest_sal` AND g.`highest_sal`;
SELECT * FROM myv2 ORDER BY ag LIMIT 1;
CREATE VIEW myv3ASSELECT * FROM myv2 ORDER BY ag LIMIT 1;SELECT d.*,m.agFROM myv3 mJOIN departments dON m.`department_id`=d.`department_id`;
/*create or replace view 视图名as查询语句;*/SELECT * FROM myv3 CREATE OR REPLACE VIEW myv3ASSELECT AVG(salary),job_idFROM employeesGROUP BY job_id;
/*语法:alter view 视图名as 查询语句;*/ALTER VIEW myv3ASSELECT * FROM employees;
/*语法:drop view 视图名,视图名,...;*/DROP VIEW emp_v1,emp_v2,myv3;
DESC myv3;SHOW CREATE VIEW myv3;
CREATE OR REPLACE VIEW myv1ASSELECT last_name,email,salary*12*(1+IFNULL(commission_pct,0)) "annual salary"FROM employees;CREATE OR REPLACE VIEW myv1ASSELECT last_name,emailFROM employees;SELECT * FROM myv1;SELECT * FROM employees;
INSERT INTO myv1 VALUES('张飞','zf@qq.com');
UPDATE myv1 SET last_name = '张无忌' WHERE last_name='张飞';
DELETE FROM myv1 WHERE last_name = '张无忌';
#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 myv1ASSELECT MAX(salary) m,department_idFROM employeesGROUP 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 myv2ASSELECT 'john' NAME;SELECT * FROM myv2;#更新UPDATE myv2 SET NAME='lucy';#③Select中包含子查询CREATE OR REPLACE VIEW myv3ASSELECT 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;#④joinCREATE OR REPLACE VIEW myv4ASSELECT last_name,department_nameFROM employees eJOIN departments dON 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 myv5ASSELECT * 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 myv6ASSELECT last_name,email,salaryFROM employeesWHERE 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';
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