CBSE Book Class 12 Informatic Practices RDBMS Concepts

Introduction

DBMS and Transaction Management Raunak studies in Class XII. He is very helpful. During summer vacations, he helped his aunt's son in his studies. His aunt was very pleased with him and gave him a cheque of ` 2000.00. Raunak knows that after presentation of the cheque to the bank, his aunt's account will be reduced by ` 2000.00 and his account will be increased by ` 2000.00. Raunak walked up to the bank to present the cheque. Are Raunak's fears valid? Can you recollect something like this happening with you or with your friends or relatives?

Raunak should not fear at all as the Bank's DBMS looks after these eventualities. DBMSs ensure consistency (correctness) of data by managing Transactions. Mostly customers view an operation like transfer of funds as a single operation but actually it consists of series of operations. Suppose Raunak's account number is 3246 and his aunt's account number is 5135. In order to process the cheque presented by Raunak, the following two SQL commands need to be executed on the database maintained by the bank:

What is a Transaction 

A Transaction is a unit of work that must be done in logical order and successfully as a group or not done at all. Unit of work means that a Transaction consists of different tasks - but together they are considered as one unit. Each transaction has a beginning and an end. If anything goes wrong in between the execution of transaction, the entire transaction (No matter to what extent has been done) should be cancelled. If it is successful, then the entire transaction should be saved to the database.

A transaction is a unit of work that must be done in logical order and successfully as a group or not done at all. In Raunak's case, both the updation statements constitute a transaction. Both are together treated as a single unit.

To understand how transactions are managed, let us study the following 3 statements of SQL:

   START TRANSACTION statement

   COMMIT statement

   ROLLBACK statement 

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