SQL Blog | LearnSQL.com

Can you Join two Tables Without a Common Column?

by Kateryna Koidan

6 Aug 2020 Yes, you can! The longer answer is yes, there are a few ways to combine two tables without a common column, including CROSS JOIN (Cartesian product) and UNION. The latter is technically not a join but can be handy for merging tables in SQL. In this article, I’ll guide you through the different solutions with examples. When Do you Need to Join Tables Without a Common Column? Beginners just getting started with SQL are usually introduced to standard equi joins, in which two tables are combined by a common column.

Who Should Learn SQL Window Functions?

by Tihomir Babic

5 Aug 2020 Do you want to learn how SQL window functions can help you at your job? This article will show you examples from various business applications where they can be very useful. I won’t be explaining what SQL window functions are in this article, but rather how to use them. If you’re not familiar with window functions or their syntax, don’t worry. Here’s an article that can help you with an introduction to SQL window functions.

SQL Course of the Month - Recursive Queries

by LearnSQL.com Team

4 Aug 2020 Recursive Queries is one of SQL’s more advanced features. You could say they divide SQL users into beginners and experts. But how do you learn recursive queries? And why do you need them, anyway? Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo, is here to help. In this article, she answers your questions about our August SQL Course of the Month: Recursive Queries. Recursive queries … that sounds very serious.

New Monthly Challenge for August 2020!

by LearnSQL.com Team

1 Aug 2020 A new month always brings new challenges. The August Monthly Challenge on LearnSQL.com is ready! This month, we invite you to support Mike in his first year of boarding school while testing your SQL knowledge. The SQL Challenge is a set of several exercises to help you practice your SQL skills. Each challenge is centered around a specific theme—food, stars, planets, travels, work, school, etc. The exercises within a challenge are interrelated, but you can do them in whatever order you want.

The SQL HAVING Clause Explained

by Dorota Wdzięczna

31 Jul 2020 What is the SQL HAVING clause? Why do you need it, and where do you use it? We’ll explain HAVING in detail. HAVING is a very common clause in SQL queries. Like WHERE, it helps filter data; however, HAVING works in a different way. If you are familiar with the GROUP BY clause and have only heard about HAVING – or if you’re not familiar with HAVING at all – this article is what you need.

How to Use Subqueries in INSERT, UPDATE, and DELETE Statements

by Ignacio L. Bisso

30 Jul 2020 Did you know that subqueries can also be used in UPDATE, INSERT, and DELETE statements? Subqueries in SQL are like building blocks that can be used in a variety of statements, not just SELECT. If you find subqueries useful in SELECT, read this article to find out how useful they can be in other instructions. You will be able to create much more complex and powerful SQL queries in no time!

Our 6 Favorite SQL Books for 2020

by Jakub Romanowski

29 Jul 2020 So you want to learn SQL and query databases? Great! Check out these six SQL books for an in-depth look at the language and you’ll be writing queries in no time! You take SQL courses, participate in internet discussions and forums, watch tutorials on YouTube... What else can you do to develop your skills? Sometimes it’s good to reach for old-fashioned sources of knowledge: SQL books. Which book(s) should you choose?

Who Is a Data Engineer?

by Adrian Więch

28 Jul 2020 A new kind of job has recently emerged in the IT world: Data Engineer. At first sight, it may seem very similar to Data Analyst or Data Scientist positions. However, our article explains all the important differences. We present the skills, tools, and everyday tasks of Data Engineers. We also explain how you can get started with this career path. Thirty years ago, we typically used terms such as “Computer Scientist” when referring to anyone working with computers.

What's the Difference Between Having Multiple Tables in FROM and Using JOIN?

by Kateryna Koidan

24 Jul 2020 What’s your approach to joining tables in SQL? In this article, we discuss two approaches and explain why many SQL developers have a definite preference for JOIN. Do you prefer to list multiple tables in FROM and use WHERE to set the join conditions? Or do you use the JOIN keyword? SQL supports both, but there are significant differences between them. Let’s look at each one in detail and then discuss why JOIN is generally preferred.

How to Analyze a Time Series in SQL

23 Jul 2020 Values ordered by time are called a time series. In this article, I’ll show you the most frequent patterns and teach you how to write queries for time series in SQL with the help of window functions. Maybe you’ve had the opportunity to analyze some variables where each value was associated with a time value. Such data – where values are ordered by time – is called time series data.

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