MySQL transaction

Business ： Either they all succeed 、 Or they all failed （ For example, two people transfer money ）

A set of sql Put it in a batch to execute

Business principles ：ACID principle

• Atomicity （Atomicity）： For the same transaction , Or both , Or it's not done
• Uniformity （Consistency）：（ Final consistency ） For a transaction, the state before and after the operation is consistent
• Isolation, （Isolation）： For multiple users at the same time , It is mainly to exclude the influence of other foods on this affair
• persistence （Durability）： The data after the transaction ends will not be lost due to external reasons （ The transaction was not committed , Return to the original state , The transaction has been committed , Persist to database ）

The isolation level of the transaction ：

• Dirty reading ： A transaction reads uncommitted data from another transaction
• Non repeatability ： Read a row of data in a table in a transaction , Multiple reads result is different .（ This is not necessarily a mistake , It's just that on some occasions it's not right ）
• Virtual reading （ Fantasy reading ）： It refers to the data inserted by other transactions in a transaction , Leading to inconsistent reading before and after .（ It's usually the line effect , One more line ）

Perform transactions
– mysql Automatic transaction commit is enabled by default

set autocommit = 0 /* close */
set autocommit = 1 /* Turn on （ default ）*/
--  Handle transactions manually 
--  The transaction open 
start transaction -- Mark the beginning of a transaction , From after sql All in one transaction 

insert **
insert **

--  Submit ： Persistence （ success ！）
commit

-- Roll back ： Back to the original （ Failure ！）
rollback

-- End of transaction 
set autocommit = 1 -- Turn on auto submit 

-- understand 
savepoint  Save point name  -- Set a save point for a transaction 

rollback to savepoint  Save point name  -- Roll back to savepoint 

release savepoint  Save point name  -- Undo savepoint 

Analog transfer

create database shop character set utf8 collate utf8_general_ci
use shop
create table account
(
	id int(3)not null auto_increment ,
	name varchar(20) not null,
	money decimal(9,2) not null,
	primary key (id)
)engine=InnoDB default charset = utf8;

Insert two rows of data

Simulate transfer transactions

set autocommit = 0; --1  Turn off auto submit 
start transaction --2  Start a transaction 
update account set money=money-500 where name='ming'--3
update account set money=money+500 where name='hao'--4
commit;--5
rollback;--6
set autocommit = 1;--7

One sentence at a time , In the implementation of the 3、4 After sentence , If direct commit Can not rollback.