JDBC

Transaction: a bunch of operation in logic, the unit which consists the operation will works all or breaks down all. 

Every operation of MySQL server is a independent transaction in default situation.

TPL(Transaction Processing Language):

　　start transaction

　　commit

　　rollback

SQL statement:

CREATE TABLE account(
   id INT PRIMARY KEY AUTO_INCREMENT,
   name VARCHAR(40),
   money FLOAT   
);
INSERT INTO account(name,money) VALUES('aa',1000);
INSERT INTO account(name,money) VALUES('aa',1000);
INSERT INTO account(name,money) VALUES('aa',1000);

START TRANSACTION;
UPDATE account SET money=money-100 WHERE name='aa';
UPDATE account SET money=money+100 WHERE name='bb';
COMMIT;

 JDBC code:

package com.pp.jdbc;

import java.sql.Connection;
import java.sql.PreparedStatement;
import org.junit.Test;
import com.pp.util.JdbcUtil;

public class TransactionDemo {
    @Test
    public void test1() {
        Connection connection = null;
        PreparedStatement pstatement = null;
        try {
            connection = JdbcUtil.getConnection();
            // start transaction
            connection.setAutoCommit(false);

　　　　　　　　// set the isolation level
　　　　　　　　connection.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);

            pstatement = connection
                    .prepareStatement("UPDATE accout SET money=money-100 WHERE name='aa'");
            pstatement.executeUpdate();
            pstatement = connection
                    .prepareStatement("UPDATE accout SET money=money-100 WHERE name='aa'");
            pstatement.executeUpdate();
            // commit
            connection.commit();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
        }
    }
}

 The feature of Transaction:

　　1. Atomicity: the statement in one transaction can not be seperated.

　　2. Consistency: the transaction should keep the data in database from one status to another consistent status, for example: transfer money.

　　3. Isolation: the transaction should not be disturbed or broke down when multi-thread prolems occurs.

　　4. Durability: the submited data should be stored in durability, for example: in the disk.

Transaction isolation:

　　1. If ignore the transaction isolation, will lead to the following problems:

　　　　a. Dirty read: one transaction reads the other transaction's unsubmited data

　　　　b. Non-repeatable read: one transaction reads the other transaction's submited data

　　　　c. Phantom read: one transaction reads the the other transaction's insert data

 　　2. How to controll the isolation level?

　　　　READ UNCOMMITTED: a,b,c are possible

　　　　READ COMMITTED: prevent a but b,c are possible

　　　　REPEATABLE READ: prevent a and b, but c are possible

　　　　SERIALIZEBLE: prevent a,b and c

　　MySQL's default isolation level is REPEATABLE READ

　　Oracle's default isolation level is READ COMMIETTED

　　Check current MySQL data base isolation level:

　　　　SELECT @@tx_isolation;

　　Set the current transaction's isolation level:

　　　　SET TRANSACTION ISOLATION LEVEL isolation_level_name;(must set before the current transaction starts)

 Update lost: 

　　One transaction override the other transaction's submitted data