Articles Cookbook
15 Sep 2020
Kateryna Koidan

GROUP BY in SQL Explained

The SQL GROUP BY statement is easy to use, but it can be hard to master. Learn what you can do with GROUP BY, how it works, and how to use it with aggregate functions. GROUP BY is one of the basic SQL tools. However, it might be difficult for beginners to understand how GROUP BY works and how it is used to compute statistics with different aggregate functions. In this article, I’ll use several examples to show exactly how GROUP BY organizes rows and how aggregate functions can be used to calculate statistics on one or more columns.
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11 Sep 2020
Arleta Więch

Top 5 Beginner Online SQL Courses in 2020

Looking for an exciting new career? Data analysis won’t disappoint you! The simplest way to make this possible is by learning SQL, and online SQL courses are the most effective learning method. Don’t know where to start? Here’s an overview of the best online SQL courses for complete beginners. There are infinite reasons for changing your industry. You may want to land a new job because you’re burnt out. You may be bored and want something more challenging.
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10 Sep 2020
Agnieszka Kozubek-Krycuń

Creating SQL Courses: Behind the Scenes at LearnSQL.com

Take a peek behind the scenes and learn our secret for creating great SQL courses! Have you ever wondered how LearnSQL.com courses are created? Are we looking at a lot of hard work or just a bit of magic? Or maybe both? Here’s a hint: we rely on proven methods to create user-friendly online courses. But it’s not easy! Read on to see the 8 steps we take when creating a new SQL course.
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9 Sep 2020
Rebecca McKeown

Why and How to Find Freelance SQL Jobs

If Covid-19 has you all “I-want-to-stop-working-for-the-man-and-enjoy-a-more-fulfilling-life-as-the-master-of-my-own-destiny”, then I’ve got news for you. Not only is it possible to be an SQL freelancer, it’s also a potentially lucrative and liberating career move. It will allow you to work for a diverse range of clients and march to the beat of your own drum. Of course, SQL freelancing isn’t for everyone. You will need a strong sense of self-motivation, some serious hustling skills, and the ability to sell yourself and your services as THE ABSOLUTE BEST all the time, every time - day in, day out.
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8 Sep 2020
Dorota Wdzięczna

Seven Examples Using MySQL Window Functions

Window functions are an advanced SQL feature available in most popular databases. MySQL had not supported them for a long time, but that changed in Version 8.0. They are helpful not only for analysts and people who create reports, but also for other professionals who use databases to select data needed. In this article, we explain the syntax of some popular window functions with practical examples. What Is a Window Function?
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4 Sep 2020
Marija Ilic

What a Moving Average Is and How to Compute it in SQL

Want to dive deep into time series data and examine long-term trends? Want to know what a moving average is and how to compute it in SQL? Then this article is for you. I’ll explain a powerful feature in SQL called window functions and show how you can calculate moving averages using them. The best way to learn about SQL window functions is the interactive Window Functions course at LearnSQL.
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2 Sep 2020
Zahin Rahman

How to Find Duplicate Values in SQL — The Ultimate Guide

Find duplicate values in SQL efficiently and avoid wasting resources. This article demonstrates how to locate and address duplicate records using SQL's GROUP BY and HAVING clauses. Database best practices usually dictate having unique constraints (such as the primary key) on a table to prevent the duplication of rows when data is extracted and consolidated. However, you may find yourself working on a dataset with duplicate rows. This could be because of human error, an application bug, or uncleaned data that’s been extracted and merged from external sources, among other things.
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1 Sep 2020
LearnSQL.com Team

Course of the Month: Analyzing Revenue Trends in SQL

We work hard, we learn SQL, and we develop professionally. But why? For our own satisfaction, but also for money! The knowledge of SQL will increase your income significantly. If you are proficient in SQL, you can better analyze your company's revenue. How? I asked Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo. In this article, she answers your questions about our September SQL Course of the Month: Analyzing Revenue Trends in SQL.
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28 Aug 2020
Adrian Więch

How CTEs Work

The SQL language offers a feature named Common Table Expressions, or CTEs. Also known as WITH clauses, CTEs are a fairly new addition to SQL. They help you break longer queries into smaller chunks, making your queries much easier to understand. Read the article to find out how to use CTEs and how they differ from traditional subqueries. Common Table Expressions (CTEs), which are essentially named subqueries, were first mentioned in the SQL standard between 1999 and 2000.
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27 Aug 2020
Ignacio L. Bisso

How Does SQL GROUP BY Work?

Grouping results is a powerful SQL feature that allows you to compute key statistics for a group of records. GROUP BY is one of SQL’s most powerful clauses. It allows you to see data in a new way and find key metrics (like the average, maximal, and minimal values in a group of records). Without GROUP BY, all the results we obtain are oriented to records. With GROUP BY, we can create groups of records and calculate metrics on each group.
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