演示不同隔离级别下的并发问题 1.当把事务的隔离级别设置为read uncommitted ,会引发脏读,不可重复读,虚读 A窗口 start transaction isolation level read uncommitted; start transaction; select * from account; =======这个时候发现aaa的账户是1000元
演示不同隔离级别下的并发问题
1.当把事务的隔离级别设置为read uncommitted ,会引发脏读,不可重复读,虚读
A窗口
start transaction isolation level read uncommitted;
start transaction;
select * from account;
=======这个时候发现aaa的账户是1000元,转到B窗口
select * from acount where name=='aaa';
=======发现aaa的账户多了100元,这个时候a窗口读到的数据时b窗口未提交的数据(脏读);
B窗口
start transaction;(有这句话,不写commit语句,数据是不会提交到数据库的)
update account set money=money+100 where name='aaa';
------不要提交,转到A窗口查询
2..当把事务的隔离级别设置为read committed ,会引发不可重复读,虚读,但可避免脏读;
A窗口
start transaction isolation level read committed;
start transaction;
select * from account;
=======这个时候发现aaa的账户是1000元,转到B窗口
select * from acount where name=='aaa';
=======发现aaa的账户多了100元,这个时候a窗口读到了别的事务提交的数据,两次读取到的是不同的数据(不可重复读);
B窗口
start transaction;
update account set money=money+100 where name='aaa';
commit;
-----转到a窗口
3.当把事务的隔离级别设置为repeatable read(mysql 默认级别) ,会引发虚读,但可避免脏读,不可重复读;
A窗口:
set transaction isolation level repeatable read;
start transaction ;
select * from account;
=======发现有4条记录,转到b窗口
select * from account;
========可能发现有5条记录,这时候发生了a读取到另外一个事务插入的数据(虚读)
B窗口
start transaction;
insert into acount(name,money) values('ggg',1000);
commit;
-------转到a窗口
4.当把事务的隔离级别设置为Serializable ,会避免所有的问题;
A窗口:
set transaction isolation level repeatable read;
start transaction ;
select * from account;
=======发现有4条记录,转到b窗口
B窗口
start transaction;
insert into acount(name,money) values('ggg',1000);
-------发现不能插入,只能等待a结束事务才能插入

The main role of MySQL in web applications is to store and manage data. 1.MySQL efficiently processes user information, product catalogs, transaction records and other data. 2. Through SQL query, developers can extract information from the database to generate dynamic content. 3.MySQL works based on the client-server model to ensure acceptable query speed.

The steps to build a MySQL database include: 1. Create a database and table, 2. Insert data, and 3. Conduct queries. First, use the CREATEDATABASE and CREATETABLE statements to create the database and table, then use the INSERTINTO statement to insert the data, and finally use the SELECT statement to query the data.

MySQL is suitable for beginners because it is easy to use and powerful. 1.MySQL is a relational database, and uses SQL for CRUD operations. 2. It is simple to install and requires the root user password to be configured. 3. Use INSERT, UPDATE, DELETE, and SELECT to perform data operations. 4. ORDERBY, WHERE and JOIN can be used for complex queries. 5. Debugging requires checking the syntax and use EXPLAIN to analyze the query. 6. Optimization suggestions include using indexes, choosing the right data type and good programming habits.

MySQL is suitable for beginners because: 1) easy to install and configure, 2) rich learning resources, 3) intuitive SQL syntax, 4) powerful tool support. Nevertheless, beginners need to overcome challenges such as database design, query optimization, security management, and data backup.

Yes,SQLisaprogramminglanguagespecializedfordatamanagement.1)It'sdeclarative,focusingonwhattoachieveratherthanhow.2)SQLisessentialforquerying,inserting,updating,anddeletingdatainrelationaldatabases.3)Whileuser-friendly,itrequiresoptimizationtoavoidper

ACID attributes include atomicity, consistency, isolation and durability, and are the cornerstone of database design. 1. Atomicity ensures that the transaction is either completely successful or completely failed. 2. Consistency ensures that the database remains consistent before and after a transaction. 3. Isolation ensures that transactions do not interfere with each other. 4. Persistence ensures that data is permanently saved after transaction submission.

MySQL is not only a database management system (DBMS) but also closely related to programming languages. 1) As a DBMS, MySQL is used to store, organize and retrieve data, and optimizing indexes can improve query performance. 2) Combining SQL with programming languages, embedded in Python, using ORM tools such as SQLAlchemy can simplify operations. 3) Performance optimization includes indexing, querying, caching, library and table division and transaction management.

MySQL uses SQL commands to manage data. 1. Basic commands include SELECT, INSERT, UPDATE and DELETE. 2. Advanced usage involves JOIN, subquery and aggregate functions. 3. Common errors include syntax, logic and performance issues. 4. Optimization tips include using indexes, avoiding SELECT* and using LIMIT.


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