MySQL Transactions

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Information about MySQL Transactions
Technology

Published on October 7, 2013

Author: reggieniccolosantos

Source: slideshare.net

Description

MySQL Transactions
- Definition
- Sample scenario
- Properties (ACID)
- Syntax
- Example

MySQL Transactions Reggie Niccolo Santos UP ITDC

Outline  What are transactions?  Sample scenario  Properties (ACID)  Syntax  Example

What are transactions?  Sequential group of DML statements, which is performed as if it were one single work unit  Will never complete unless each individual operation within the group is successful. If any operation within the transaction fails, the entire transaction will fail

What are transactions?  Begins with the first executable SQL statement  Ends when it is committed or rolled back, either explicitly with a COMMIT or ROLLBACK statement or implicitly when a DDL statement is issued

Sample Scenario Suppose a bank customer transfers money from his savings account (SB a/c) to his current account (CA a/c), the statement will be divided into four blocks:  Debit SB a/c  Credit CA a/c  Record in Transaction Journal  End Transaction

Sample Scenario The SQL statement to debit SB a/c is as follows: UPDATE sb_accounts SET balance = balance - 1000 WHERE account_no = 932656;

Sample Scenario The SQL statement to credit CA a/c is as follows: UPDATE ca_accounts SET balance = balance + 1000 WHERE account_no = 933456;

Sample Scenario The SQL statement for recording in the transaction journal is as follows: INSERT INTO journal VALUES (100896, 'Transaction on Benjamin Hampshair a/c', '26-AUG-08' 932656, 933456, 1000);

Sample Scenario The SQL statement for End Transaction is as follows: COMMIT WORK;

Properties (ACID)  Atomicity − Ensures that all operations within the work unit are completed successfully; otherwise, the transaction is aborted at the point of failure and previous operations are rolled back to their former state

Properties (ACID)  Consistency − Ensures that the database properly changes states upon a successfully committed transaction

Properties (ACID)  Isolation − Enables transactions to operate independently of and transparent to each other

Properties (ACID)  Durability − Ensures that the result or effect of a committed transaction persists in case of a system failure

Syntax START TRANSACTION [transaction_characteristic [, transaction_characteristic] ...] transaction_characteristic: WITH CONSISTENT SNAPSHOT | READ WRITE | READ ONLY BEGIN [WORK] COMMIT [WORK] [AND [NO] CHAIN] [[NO] RELEASE] ROLLBACK [WORK] [AND [NO] CHAIN] [[NO] RELEASE] SET autocommit = {0 | 1}

Example START TRANSACTION; SELECT @A:=SUM(salary) FROM employee_salary WHERE type=1; UPDATE salary_report SET summary=@A WHERE type=1; COMMIT;

References  Http://www.tutorialspoint.com/mysql/mysql-transactions.htm  Http://www.w3resource.com/mysql/mysql-transaction.php

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