SQL Primer: An Accelerated Introduction to SQL Basics

©  Rahul Batra 2018

Rahul BatraSQL Primerhttps://doi.org/10.1007/978-1-4842-3576-8_11

11. Understanding Joins

Rahul Batra¹ 

(1)

Gurgaon, Haryana, India

 

A join operation allows you to retrieve data from multiple tables in a single SELECT query. Two tables can be joined by a single join operator, but the result can be joined again with other tables. There must exist a same or similar column between the tables being joined.

When you design an entire database system using good design principles like normalization , we often require the use of joins to give a complete picture to a user's query. For example, we split our programming languages table into two in Chapter 7 – one holding the author details (Table 11-2) and the other holding information about ...