MySQL transaction

MySQL Business

Business (Transaction): A transaction is a complete business logic unit , Can not be further divided ;

example : Bank account transfer ,A Transfer the account to B Account 10000, You need to perform two update sentence

update Table name set Field = Field -10000 where Account id=A;

update Table name set Field = Field +10000 where Account id=B;

The above two statements must succeed or fail at the same time , One success and one failure are not allowed

To ensure that the above statements succeed or fail at the same time , Must use database " Transaction mechanism "

Only DML Statement to support transactions

DML Data operation language , Manipulate the data in the table , Connected to business (insert/delete/update);

Things exist to ensure data integrity and security ;

Suppose all businesses can use one DML No transaction mechanism is required for statement completion ;

How things work

Suppose one thing , You need to execute a insert, One more thing update, Finally, execute delete

Turn on the transaction mechanism ( Start )

perform insert sentence —> After successful execution , The execution is recorded in the operation history of the database , Data is not saved to the file , Will not really save to the hard disk ;

perform update sentence –>…;

perform delete sentence —>…;

Commit transaction commit Or roll back the transaction rollback( One of the two , Everything will end )

The four characteristics of affairs ACID

A: Atomicity : The smallest unit of things , Can not be further divided ;

C: Uniformity : Transactions must guarantee multiple DML Statements succeed or fail at the same time ;

I: Isolation, : Business A And business B Isolation between ;

D: persistence : The final data must be persisted to the hard disk file , It's the end of the business ;

The isolation of things

The isolation of things can be divided into 4 individual :

First level	Read uncommitted (read uncommitted)	The other party's affairs have not been submitted , The current transaction can read the data not submitted by the other party ; There is dirty reading (Dirty Read) The phenomenon : Indicates that dirty data has been read ( Unstable data )
The second level	Read submitted (read committed)	You can only read the data after the other party's transaction is committed , It can't be read repeatedly , Solve the dirty reading phenomenon ;
The third level	Repeatable (repeatable read)	Solved the unrepeatable read problem , The data read is fantasy ;
Level 4	serialize / Serialization	All problems solved , Low efficiency , Transaction queuing is required ;

Oracle The default isolation level of the database is : Read submitted ;

MySQL The default isolation level of the database is : Repeatable ;

// Set the isolation level of the transaction 
set global transaction isolation level read uncommitted;// Read uncommitted 
set global transaction isolation level read committed;// Read submitted 
set global transaction isolation level repeatable read;// Repeatable 
set global transaction isolation level serializable;// Serialization or serialization 
// View transaction isolation level 
select @@global.tx_isolation;

Automatic submission

MySQL Transactions are automatically committed by default ( Execute any one DML Statement is submitted once )

Turn off auto commit and turn on transactions :start transaction;

Save it :savepoint Custom location name ;

Rollback to the specified location :rollback Save it ;

The flow of a transaction

//1. Log in to the database ;
//2. Open database ;
//3. Set the transaction isolation level ;
set global transaction isolation level  Level type ;
//4. Query transaction level 
select @@global.tx_isolation;
//5. Turn off auto submit 
start transaction;
//6.DML Statement operation 
//7.rollback Rollback or commit Submit 

MySQL Remote login

command ：mysql -hhost -uusername -ppassword

host： Remote host address

username： user name

password： password