Book Image

The Data Wrangling Workshop - Second Edition

By : Brian Lipp, Shubhadeep Roychowdhury, Dr. Tirthajyoti Sarkar
Book Image

The Data Wrangling Workshop - Second Edition

By: Brian Lipp, Shubhadeep Roychowdhury, Dr. Tirthajyoti Sarkar

Overview of this book

While a huge amount of data is readily available to us, it is not useful in its raw form. For data to be meaningful, it must be curated and refined. If you’re a beginner, then The Data Wrangling Workshop will help to break down the process for you. You’ll start with the basics and build your knowledge, progressing from the core aspects behind data wrangling, to using the most popular tools and techniques. This book starts by showing you how to work with data structures using Python. Through examples and activities, you’ll understand why you should stay away from traditional methods of data cleaning used in other languages and take advantage of the specialized pre-built routines in Python. Later, you’ll learn how to use the same Python backend to extract and transform data from an array of sources, including the internet, large database vaults, and Excel financial tables. To help you prepare for more challenging scenarios, the book teaches you how to handle missing or incorrect data, and reformat it based on the requirements from your downstream analytics tool. By the end of this book, you will have developed a solid understanding of how to perform data wrangling with Python, and learned several techniques and best practices to extract, clean, transform, and format your data efficiently, from a diverse array of sources.
Table of Contents (11 chapters)

Relation Mapping in Databases

We have been working with a single table and altering it, as well as reading back the data. However, the real power of an RDBMS comes from the handling of relationships among different objects (tables). In this section, we are going to create a new table called comments and link it with the user table in a 1: N relationship. This means that one user can have multiple comments. The way we are going to do this is by adding the user table's primary key as a foreign key in the comments table. This will create a 1: N relationship.

When we link two tables, we need to specify to the database engine what should be done if the parent row is deleted, which has many children in the other table. As we can see in the following diagram, we are asking what happens at the place of the question marks when we delete row1 of the user table:

Figure 8.6: Illustration of relations

In a non-RDBMS situation, this situation can quickly become difficult...