Book Image

SQL for Data Analytics - Third Edition

By : Jun Shan, Matt Goldwasser, Upom Malik, Benjamin Johnston
Book Image

SQL for Data Analytics - Third Edition

By: Jun Shan, Matt Goldwasser, Upom Malik, Benjamin Johnston

Overview of this book

Every day, businesses operate around the clock, and a huge amount of data is generated at a rapid pace. This book helps you analyze this data and identify key patterns and behaviors that can help you and your business understand your customers at a deep, fundamental level. SQL for Data Analytics, Third Edition is a great way to get started with data analysis, showing how to effectively sort and process information from raw data, even without any prior experience. You will begin by learning how to form hypotheses and generate descriptive statistics that can provide key insights into your existing data. As you progress, you will learn how to write SQL queries to aggregate, calculate, and combine SQL data from sources outside of your current dataset. You will also discover how to work with advanced data types, like JSON. By exploring advanced techniques, such as geospatial analysis and text analysis, you will be able to understand your business at a deeper level. Finally, the book lets you in on the secret to getting information faster and more effectively by using advanced techniques like profiling and automation. By the end of this book, you will be proficient in the efficient application of SQL techniques in everyday business scenarios and looking at data with the critical eye of analytics professional.
Table of Contents (11 chapters)
9. Using SQL to Uncover the Truth: A Case Study

8. Performant SQL

Activity 8.01: Query Planning


  1. Open PostgreSQL with psql and connect to the sqlda database.
  2. Use the EXPLAIN command to return the query plan for selecting all available records within the customers table:
    SELECT * 
    FROM customers;
  3. Read the output of the plan and determine the total query cost, the setup cost, the number of rows to be returned, and the width of each row.

The output is as follows:

Seq Scan on customers  (cost=0.00..1535.00 rows=50000 width=140)

As such, the total query cost is 1535.00, the setup cost is 0.00, the number of rows to be returned is 50000, and the width of each row is 140. Your result may have numbers that are slightly different. But the general concept of measurements should be the same.

  1. Repeat the query from step 2 of this activity, this time limiting the number of returned records to 15. Review the updated query plan and compare its output against the output of the previous step...