Acid of MySQL transaction

        MYSQL In the execution of complex 、 multiple SQL when , The execution process is either fully successful , Or it's a total failure . For example, when executing multiple SQL, A few days ago SQL Successful implementation , One of the SQL collapse , And back out the data of the impact of successful execution . Let's take a bank transfer as an example ：

scene ：

         Zhang San goes to the bank counter to transfer money to Wang Wu 500 element .

software design ：

        There is an account form （acc）, Storage is ： Account No (acc_no)、 Available balance (surplus).

Transfer logic ：

        1、 Judge whether Zhang San's account balance is greater than 500 element

        2、 Zhang San's account balance minus 500 element

        3、 Add... To Wang Wu's account 500 element

    Convert to SQL as follows ：

        1）SELECT surplus FROM acc WHERE acc_no=' Zhang San's account ';
        2）UPDATE FROM acc SET surplus=surplus-500 WHERE acc_no=' Zhang San's account ';
        3）UPDATE FROM acc SET surplus=surplus+500 WHERE acc_no=' Wang Wu account ';

In the previous scenario, if there was no transaction mechanism , If we are transferring money, we may be implementing Article 2 SQL Failure , This will not affect the available balance of Wang Wu's account , But in Implementing Article 3 SQL Execution failed , It will lead to less Zhang San 500 Yuan , Wang Wu didn't receive this 500 Yuan . Transactions are very important in manipulating data .

A strict transaction support must follow ACID;

Atomicity （Atomicity）
         Atomicity means that a transaction is an indivisible unit of work , Either the operations in the transaction occur , Or none at all .
Uniformity （Consistency）
         The total weight of the data in the database changes from one complete and consistent state to another . After the transaction is executed, Zhang San either transfers money successfully , Own account is small 500, Wang Wu has many accounts 500; Keep the available balance of the account unchanged .
Isolation, （Isolation）
         Transaction isolation is when multiple users access the database concurrently , A transaction opened by a database for each user , Can't be disturbed by the operation data of other transactions , Multiple concurrent transactions should be isolated from each other . When no more operations can be performed , Others also operate on your data , Non isolation between transactions leads to
persistence （Durability）
         Persistence means that once a transaction is committed , It changes the data in the database permanently , Next, even if the database fails, it should not have any impact