RDBMS Fundamentals:

An RDBMS, or Relational Database Management System, is a specific type of database that organizes data in a structured way, using tables and relationships between them.

Table:

Table is the fundamental building block for storing and organizing data. It’s essentially a two-dimensional structure consisting of rows and columns, similar to a spreadsheet.

Columns (Fields): Each vertical column represents a specific attribute or characteristic of the data. For example, in a “Employee” table, columns might include “EmployeeID,” “FirstName,” “LastName,” “Email,” and “Address.”

Rows (Records): Each horizontal row represents a single, unique record of data. For example, in a “Employee” table, each row would contain information about a specific customer.

What is NULL Value?

A NULL value represents the absence of a value, unknown information, or an intentional omission in a field of a table. It’s distinct from an empty string or zero, as it denotes the lack of any value whatsoever.

Common scenarios for NULL:

Missing Information: A customer’s middle name might be unknown, so the corresponding field would be NULL.

Non-applicable Data: An employee’s commission might not be applicable for their role, so the commission field would be NULL.

Optional Fields: A database might allow optional fields for addresses or phone numbers, which could be NULL if not provided.

Incomplete Data Entry: Values might be missing due to incomplete data entry or errors.