Teradata - Relational Concepts


Relational Database Management System (RDBMS) is a DBMS software that helps to interact with databases. They use Structured Query Language (SQL) to interact with the data stored in tables.


Database is a collection of logically related data. They are accessed by many users for different purposes. For example, a sales database contains entire information about sales which is stored in many tables.


Tables is the basic unit in RDBMS where the data is stored. A table is a collection of rows and columns. Following is an example of employee table.

EmployeeNo FirstName LastName BirthDate
101 Mike James 1/5/1980
104 Alex Stuart 11/6/1984
102 Robert Williams 3/5/1983
105 Robert James 12/1/1984
103 Peter Paul 4/1/1983


A column contains similar data. For example, the column BirthDate in Employee table contains birth_date information for all employees.



Row is one instance of all the columns. For example, in employee table one row contains information about single employee.

EmployeeNo FirstName LastName BirthDate
101 Mike James 1/5/1980

Primary Key

Primary key is used to uniquely identify a row in a table. No duplicate values are allowed in a primary key column and they cannot accept NULL values. It is a mandatory field in a table.

Foreign Key

Foreign keys are used to build a relationship between the tables. A foreign key in a child table is defined as the primary key in the parent table. A table can have more than one foreign key. It can accept duplicate values and also null values. Foreign keys are optional in a table.