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

1. MySQL Transactions
Reggie Niccolo Santos
UP ITDC

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

3. 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

4. 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

5. 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

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

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

8. 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);

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

10. 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

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

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

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

14. 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}

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

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