Articles Cookbook
24 Jul 2020
Kateryna Koidan

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

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.
Read more
23 Jul 2020
Marija Ilic

How to Analyze a Time Series in SQL

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.
Read more
22 Jul 2020
LearnSQL.com Team

LearnSQL.com’s New Learning Path: Data Engineering

Calling all future data engineers! Would you like to learn to use SQL? Then our new Data Engineering Learning Path is just for you! We’re very excited to announce the release of a new learning path at LearnSQL.com: Data Engineering, published in July 2020. This is the second learning path offered in our platform. So far, we offered an analytical path, SQL Querying & Reporting, that focuses on writing queries and business reports in SQL.
Read more
21 Jul 2020
Zahin Rahman

Using GROUP BY in SQL

Now that you know SQL’s core commands, power up your queries with the GROUP BY clause and aggregate functions. GROUP BY is a SQL clause that arranges data into groups based on a common value (or values). It is widely used to obtain summary information for large datasets as well as for computing basic aggregate statistics. Once you have grasped SQL’s basic commands like SELECT, WHERE, and JOIN, mastering the GROUP BY clause can help you implement your SQL knowledge in real-world business intelligence scenarios.
Read more
17 Jul 2020
Dorota Wdzięczna

The LAG Function and the LEAD Function in SQL

LAG() and LEAD() are positional functions. A positional function is a type of window function. If you are not familiar with when and how to use them, what the syntax of each function is, why you might want to use them, and what the differences are, read on! LAG() and LEAD() are positional functions. These are window functions and are very useful in creating reports, because they can refer to data from rows above or below the current row.
Read more
16 Jul 2020
Tihomir Babic

When Should I Use a Common Table Expression (CTE)?

Interested in hearing more about common table expressions or CTEs? Would you like to know when CTEs are useful? Read on—we’ll discuss in this article. If you’ve heard of common table expressions, you’ve probably wondered what they do. Even if you have not, it’s good that you’re here! CTEs can be very useful, especially if you have already mastered the basics of SQL, such as selecting, ordering, filtering data, and joining tables.
Read more
15 Jul 2020
Jakub Romanowski

How to Learn SQL Fast

Are you in a rush to boost your data analysis capabilities? In this article, I'll show you how to learn SQL fast and become the Vin Diesel of data – how to become the "Fast and Querious". Step into the world of SQL with the easy-to-follow SQL from A to Z learning track from LearnSQL.com. Perfect for beginners with no IT background, this interactive series offers 7 hands-on courses where you learn by doing.
Read more
14 Jul 2020
Ignacio L. Bisso

How to Calculate the Difference Between Two Rows in SQL

Calculating the difference between two rows in SQL can be a challenging task. It is possible – and there’s more than one way to do it. In this article, I’ll explain how to use the SQL window functions LEAD() and LAG() to find the difference between two rows in the same table. The best way to learn window functions is our interactive Window Functions course. It contains over 200 hands-on exercise that will teach you all window functions concepts, from simple OVER() clause to complex topics such as combining window functions and GROUP BY clause.
Read more
10 Jul 2020
Adrian Więch

What Is Data Engineering?

Data Engineering is a fairly new term in IT. And it’s getting more and more attention. You may have heard about a few similar fields like data science, Big Data, and machine learning. This article explains the difference between these concepts and shows how they can be combined to analyze vast amounts of data. When computers first appeared, their storage capacity was very limited. Do you remember floppy disks? They were popular in the late 20th century and typically offered around 1.
Read more
9 Jul 2020
Marija Ilic

What Is a CTE?

After mastering statements like SELECT, DELETE, INSERT, and GROUP BY, you might search for ways to improve code maintainability, reproducibility, and readability. At that point, you will probably start learning about modern SQL concepts that were introduced in the early 2000s. One such SQL technique is the CTE? (common table expression) —?a temporary named result set. In this article, you will learn what a CTE is and how to use it to improve the maintenance and the readability of your code.
Read more