Book Image

SQL Query Design Patterns and Best Practices

By : Steve Hughes, Dennis Neer, Dr. Ram Babu Singh, Shabbir H. Mala, Leslie Andrews, Chi Zhang
5 (1)
Book Image

SQL Query Design Patterns and Best Practices

5 (1)
By: Steve Hughes, Dennis Neer, Dr. Ram Babu Singh, Shabbir H. Mala, Leslie Andrews, Chi Zhang

Overview of this book

SQL has been the de facto standard when interacting with databases for decades and shows no signs of going away. Through the years, report developers or data wranglers have had to learn SQL on the fly to meet the business needs, so if you are someone who needs to write queries, SQL Query Design and Pattern Best Practices is for you. This book will guide you through making efficient SQL queries by reducing set sizes for effective results. You’ll learn how to format your results to make them easier to consume at their destination. From there, the book will take you through solving complex business problems using more advanced techniques, such as common table expressions and window functions, and advance to uncovering issues resulting from security in the underlying dataset. Armed with this knowledge, you’ll have a foundation for building queries and be ready to shift focus to using tools, such as query plans and indexes, to optimize those queries. The book will go over the modern data estate, which includes data lakes and JSON data, and wrap up with a brief on how to use Jupyter notebooks in your SQL journey. By the end of this SQL book, you’ll be able to make efficient SQL queries that will improve your report writing and the overall SQL experience.
Table of Contents (21 chapters)
Part 1: Refining Your Queries to Get the Results You Need
Part 2: Solving Complex Business and Data Problems in Your Queries
Part 3: Optimizing Your Queries to Improve Performance
Part 4: Working with Your Data on the Modern Data Platform

Using the CASE statement

A CASE statement is a widely used expression that takes in a list of conditions, evaluates the database column(s) referred to in the expression and, based on the evaluation of the field value, returns transformed values according to the rules defined.

It is a powerful and versatile tool that can be used to evaluate multiple conditions and return different results based on those conditions. It can be especially useful in scenarios where we need to handle different data types or values in a flexible and efficient way. It can be used in a few places in a SQL statement.

In this section, we’ll go through a few examples to showcase how to use it in SELECT, ORDER BY, UPDATE, and HAVING.

Using a simple CASE expression in a SELECT statement

The first way to use this expression is a simple version where the expression only looks at one field and only searches for the value from that field:

SELECT TOP(3) [Stock Holding Key], [Bin Location], [BinLocationDetailed...