Chapter 15 .事务&&视图
2018-10-04 本文已影响6人
GeekGray
Chapter 15 .事务&&视图
TCL
/*
Transaction Control Language 事务控制语言
事务：
一个或一组sql语句组成一个执行单元，这个执行单元要么全部执行，要么全部不执行。
案例：转账
张三丰 1000
郭襄 1000
update 表 set 张三丰的余额=500 where name='张三丰'
意外
update 表 set 郭襄的余额=1500 where name='郭襄'
事务的特性：
- ACID
- 原子性：一个事务不可再分割，要么都执行要么都不执行
- 一致性：一个事务执行会使数据从一个一致状态切换到另外一个一致状态
- 隔离性：一个事务的执行不受其他事务的干扰
- 持久性：一个事务一旦提交，则会永久的改变数据库的数据.
事务的创建
隐式事务：事务没有明显的开启和结束的标记
比如insert、update、delete语句
delete from 表 where id =1;
显式事务：事务具有明显的开启和结束的标记
前提：必须先设置自动提交功能为禁用
set autocommit=0;
步骤1：开启事务
set autocommit=0;
start transaction;可选的
步骤2：编写事务中的sql语句(select insert update delete)
语句1;
语句2;
...
步骤3：结束事务
commit;提交事务
rollback;回滚事务
savepoint 节点名;设置保存点
mysql中默认 第三个隔离级别 repeatable read
oracle中默认第二个隔离级别 read committed
查看隔离级别
select @@tx_isolation;
设置隔离级别
set session|global transaction isolation level 隔离级别;
开启事务的语句;
update 表 set 张三丰的余额=500 where name='张三丰'
update 表 set 郭襄的余额=1500 where name='郭襄'
结束事务的语句;
*/
SHOW VARIABLES LIKE 'autocommit';
SHOW ENGINES;
1.演示事务的使用步骤
开启事务
SET autocommit=0;
START TRANSACTION;
编写一组事务的语句
UPDATE account SET balance = 1000 WHERE username='张无忌';
UPDATE account SET balance = 1000 WHERE username='赵敏';
结束事务
ROLLBACK;
commit;
SELECT * FROM account;
2.演示事务对于delete和truncate的处理的区别
SET autocommit=0;
START TRANSACTION;
DELETE FROM account;
ROLLBACK;
3.演示savepoint 的使用
SET autocommit=0;
START TRANSACTION;
DELETE FROM account WHERE id=25;
SAVEPOINT a;#设置保存点
DELETE FROM account WHERE id=28;
ROLLBACK TO a;#回滚到保存点
SELECT * FROM account;
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','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
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';
