A Point of Sale or Point of Service is generally a machine which calculate the amount of item/services a customer owed to the trader. A customer can pay in cash or via a credit card.
When you make a Left Join or make a UNION query the DBMS will put NULL where their is no match in the set. This tutorial is aimed to discuss the options by which NULL can be substituted with 0 in MySQL DBMS.
A Database is required to support an Online school system which should be so generic that any number of schools in an area, (eg Town/country/world) can register to use the System.