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 ISNULL() function

The ISNULL() function is used to return the defined input value in case the passed-in expression has NULL as its value. It only accepts two parameters and only evaluates the passed-in expression. We will walk through a few simple examples of it and do a comparison between ISNULL() and COALESCE() in this section.

How to use ISNULL()

Let’s jump into the examples!

Run the following code in SSMS:

SELECT ISNULL('Hello', 'World') AS [Output]

The result returned is as follows:

Figure 4.14 – Result of the query

Figure 4.14 – Result of the query

As we can see, when we pass in two VARCHAR values, the function evaluates the first one (in this case, Hello) and determines it is not a NULL value, so it returns the Hello value itself as result.

Now, run the following chunk of code:

SELECT ISNULL(NULL, 'World') AS [Output]

The result we get this time is as follows:

Figure 4.15 – Result of the query

Figure 4.15 –...