Concepts of Relational database system

To understand the basic concepts of RDBMS,the following information is provided to you.

Table is the place where you can save all your data in the relational model(RDBMS). Data is organized in terms of Rows and columns in a table. For Example, see the information we have here in employee table.

EMPLOYEE TABLE : (With out Relational Model)

In the above example,we have 6 employee records. 2 employees for each department.Take a look at it and see how many times we have the same information ie duplicate information.
The departments are occuring twice and so more memory space is occupied. To calculate this,

For 6 records we wasted 26 bytes, Imagine having 5000 employees working in the
company! Then we are wasting 28 * 5000 bytes = 140000bytes,which is around 13 MB of memory.

Advantages of the new system(Relational model):

• If you split the above shown data into two different tables then it becomes easy to maintain the data, For example:- If a particular department moved from Dallas to Atlanta,we need to change the city table for deptno 10 in the new system where as in the previous system we have to update all the employee records whose department is deptno 10.
• removes the duplicate information (Data Redundancy) instead of duplicating the Department name and Location for every employee record as seen in the previous system,You can see Department name and Location only once in the Department table based on the common column in the new system .
• Reduces the Memory space in the database

Employee Table

Department Table

We have the same information now as before but the difference is we have two tables instead of one table.
To relate the two tables, we need a common column between the tables. In the above example, there is a common column (DEPTNO).