Articles Cookbook
23 Feb 2022
LearnSQL.com Team

Monthly SQL Practice in 2022 & 2021 Compilation Courses

Are you looking for ways to practice SQL? Tired of boring exercises based on unreal scenarios? We have something for you! Every month, we publish a new set of SQL practice exercises. You'll find all of them in the monthly SQL Practice. Here at LearnSQL.com, we believe the best way to learn SQL is through practice. All of our SQL courses (and there are over 30 of them!) are hands-on.
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22 Feb 2022
Dominika Florczykowska

An Overview of MySQL Data Types

What data types are available in a MySQL database? In this article, you’ll learn about numeric data types, text data types, and much more! You may have seen our article about data types in SQL. Here, we focus on the MySQL data types. We will discuss the most commonly used ones: numeric, text, and date and time. If you are interested in the topic, be sure to check out our Data Types in SQL course.
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15 Feb 2022
Kateryna Koidan

How to Keep Unmatched Rows From Two Tables in a SQL JOIN

Are you looking to join two tables in SQL without removing unmatched rows? Do you want to keep unmatched rows from one or both tables? In this article, I’ll explain how to keep all the records you want by using outer JOINs, such as LEFT JOIN, RIGHT JOIN, and FULL JOIN. Examples included! The SQL JOIN is a powerful tool that helps you combine data from multiple tables of your database.
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10 Feb 2022
Tihomir Babic

How to Query a Parent-Child Tree in SQL

What are parent-child tree structures in SQL? In this article, we answer that question, talk about query hierarchy, and demonstrate the five most common SQL queries you’ll need for these data structures. Yes, you can use SQL on a parent-child tree structure. I’ll show you how in this article. Along the way, I’ll walk you through five query examples, starting with the easiest and ending with the most complex.
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8 Feb 2022
Himanshu Kathuria

What Is the Future of the Data Engineer?

If you are wondering about the future of data engineering as a career and whether it is worth becoming a data engineer, then this article is for you. Here, I cover how lucrative the prospects are for data engineering and how you can get started and thrive in the domain. “Data” is probably one of the most used terms in our everyday business language today. A data engineer plays a pivotal role in developing the infrastructure required for data-related actions.
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3 Feb 2022
Karolina Niewiarowska

Is Learning PostgreSQL in 2022 Worthwhile?

You want to take a SQL course, but selecting the right one can be too challenging. Perhaps you don't know which dialect you should start with? PostgreSQL is one of the best options. Check out if it is worth it to learn PostgreSQL in 2022. When you search the web, there are many job advertisements for database specialists. Perhaps that is why you have chosen the direction toward development. Or maybe you are just fed up with Excel in your day-to-day duties (which is not surprising) and want to make work easier.
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27 Jan 2022
Kateryna Koidan

How Do You Get Rid of Duplicates in an SQL JOIN?

Do you have unwanted duplicates from your SQL JOIN query? In this article, I’ll discuss the possible reasons for getting duplicates after joining tables in SQL and show how to fix a query depending on the reason behind the duplicates. Data analysts with little experience in SQL JOINs often encounter unwanted duplicates in the result set. It’s challenging for beginners to identify the reason behind these duplicates in JOINs.
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25 Jan 2022
Tihomir Babic

The SQL OVER() Clause Explained

Here is a detailed explanation of the OVER() clause in SQL window functions. This is a detailed guide on using the OVER() clause in SQL window functions. I will focus specifically on this clause, which requires that you have at least a general idea of how window functions work. To make the best out of this article, take a look at the SQL Window Functions Cheat Sheet. Feel free to have it by your side as we go.
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20 Jan 2022
Andrew Bone

10 PostgreSQL Interview Questions and Answers

Job interviews are always stressful. Interviewing and getting asked technical questions about PostgreSQL is even more of a challenge! In this article, we’ll cover some of the PostgreSQL interview questions you can expect when applying for a new job. By the end of the article, you should be able to handle most of the questions you are likely to face. We’ve previously covered common questions you can expect at a SQL job interview, but this article will be focused on Postgres specifically.
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19 Jan 2022
Ignacio L. Bisso

What Is a Common Table Expression (CTE) in SQL?

The common table expression (CTE) is a powerful construct in SQL that helps simplify a query. CTEs work as virtual tables (with records and columns), created during the execution of a query, used by the query, and eliminated after query execution. A CTE is defined using a CTE query definition, which specifies the structure and content of the CTE. CTEs often act as a bridge to transform the data in source tables to the format expected by the query.
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