RDBMS

 RDBMS

RDBMS stands for Relational DataBase Management System. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.

A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. 

What is table ?

The data in RDBMS is stored in database objects called tables. The table is a collection of related data entries and it consists of columns and rows.

Remember, a table is the most common and simplest form of data storage in a relational database. Following is the example of a CUSTOMERS table:

+----+----------+-----+-----------+----------+ | ID | NAME     | AGE | ADDRESS   | SALARY   | +----+----------+-----+-----------+----------+ |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 | |  2 | Khilan   |  25 | Delhi     |  1500.00 | |  3 | kaushik  |  23 | Kota      |  2000.00 | |  4 | Chaitali |  25 | Mumbai    |  6500.00 | |  5 | Hardik   |  27 | Bhopal    |  8500.00 | |  6 | Komal    |  22 | MP        |  4500.00 | |  7 | Muffy    |  24 | Indore    | 10000.00 | +----+----------+-----+-----------+----------+

  

What is field?

Every table is broken up into smaller entities called fields. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.

A field is a column in a table that is designed to maintain specific information about every record in the table.

What is record, or row?

A record, also called a row of data, is each individual entry that exists in a table. For example there are 7 records in the above CUSTOMERS table. Following is a single row of data or record in the CUSTOMERS table:

 

+----+----------+-----+-----------+----------+ |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 | +----+----------+-----+-----------+----------+

  

A record is a horizontal entity in a table.

What is column?

A column is a vertical entity in a table that contains all information associated with a specific field in a table.

For example, a column in the CUSTOMERS table is ADDRESS which represents location description and would consist of the following:

+-----------+ | ADDRESS   | +-----------+ | Ahmedabad | | Delhi     | | Kota      | | Mumbai    | | Bhopal    | | MP        | | Indore    | +----+------+

 

What is NULL value?

A NULL value in a table is a value in a field that appears to be blank which means A field with a NULL value is a field with no value.

It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation.