MySQL transactions

1, Concept

         A set of SQL Statements are executed in the same batch , If one SQL Statement error , Then all of the SQL Will be cancelled .

2, The characteristics of affairs

（1） Atomicity ： Transactions in the database are treated as atomic granularity , Can not be further divided , The entire statement either executes , Or not .

（2） Uniformity ： Before and after a transaction , The integrity constraints of the database do not change .

（3） Isolation, ：⼀ The execution of a transaction ⾏ No other transactions ⼲ Disturb .⼀ Operations within a transaction and make ⽤ Data is isolated from other concurrent transactions , Concurrent execution ⾏ The transactions of cannot interact with each other ⼲ Disturb .

（4） persistence ： Also called permanence , finger ⼀ One transaction ⼀ Once submitted , Its changes to the data in the database should be permanent . The following other operations or faults should not be performed ⾏ Have any effect on the result .

3, Isolation level

（1） Read uncommitted content （Read Uncommitted）

All transactions can see the results of other uncommitted transactions . Can read uncommitted data .（ Dirty reading ）

（2） Read submissions （Read Committed）

After the transaction is committed or rolled back , Can be read data .（ It can't be read repeatedly ）

（3） Repeatable （Repeatable Read）

When the database is added to the transaction of data , Can read data .（ Repeatable ）

（4） Serializable （Serializable）

When the transaction is executed , Will lock at all levels , It seems that transactions are carried out in a serial manner , Not together . There will be no conflict with each other .