Transaction is a set of one or more SQL statements that take the database from one consistent state to another. The most common example used to explain transactions is of transferring money from one account to another. Let's use this in the following example.
Let's create a table to simulate a few possible scenarios:
[root@MyCentOS ~]# psql psql (9.3.0) Type "help" for help. postgres=# CREATE USER bank PASSWORD 'bank'; CREATE ROLE postgres=# ALTER USER bank WITH createdb; ALTER ROLE postgres=# \c test bank You are now connected to database "test" as user "bank". test=> CREATE DATABASE accounts; CREATE DATABASE test=> \c accounts; You are now connected to database "accounts" as user "bank". accounts=> CREATE TABLE account (id serial PRIMARY KEY , first_name varchar(100), last_name varchar(100), account_bal numeric (10,2)); CREATE TABLE
Once this is done, we can populate the table with some data to simulate a bank with a few million customers. I used web2py...