Teradata - Relational Concepts


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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

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

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

Columns

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

BirthDate
1/5/1980
11/6/1984
3/5/1983
12/1/1984
4/1/1983

Row

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.



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