Articles Cookbook
28 Oct 2020
Tihomir Babic

What are SQL CTE Best Practices?

Are you wondering what the best practices for using common table expressions are? This article will help you learn when to use a CTE and how to write it. If you have heard about SQL CTEs, you have probably noticed they’re often mentioned together with subqueries. Sometimes, people think there’s no difference compared to the subqueries, and there’s often debate about whether a CTE or subquery should be used to get a particular result.
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27 Oct 2020
Kateryna Koidan

How to Fix a 'Not a GROUP BY Expression' Error

Whether you are an experienced SQL user or only a beginner, your SQL queries may return errors. The accompanying messages are supposed to help you fix them; however, sometimes the messages are not very helpful. The Oracle message “Not a GROUP BY expression” is one such example. Let’s review what this is about and how to fix it. We are going to assume some basic understanding of how GROUP BY works.
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23 Oct 2020
Kateryna Koidan

How to Learn SQL Common Table Expressions (CTEs)

Common table expressions are very useful for organizing, traversing, and improving the readability of long SQL queries.  Moreover, recursive CTEs, which can reference themselves, solve problems that cannot be addressed with other queries. But how do you master common table expressions in SQL? In this article, I discuss the most effective strategies for learning CTEs and suggest how to address the common challenges of learning common table expressions on your own.
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22 Oct 2020
Ignacio L. Bisso

What is a Primary Key in SQL?

Primary keys are an important concept in SQL databases. They provide a unique ID for every row in a database table. As an SQL developer, you should know what primary keys are, what data values are allowed in them, and how to create them. Read this article to learn the ABCs of primary keys in 10 minutes. How to Identify Rows in a Table Tables are the main objects in an SQL database, and as you probably know, tables store records or rows.
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21 Oct 2020
LearnSQL.com Team

Is Learning SQL for Free Worthwhile?

Everyone likes to get something for free, even when it comes to SQL courses. But is free always good? Find out how and where you can learn SQL for free – in a way that’s worth your time. Beginner-friendly database courses and SQL tutorials often promise to teach SQL fundamentals like SELECT, WHERE, GROUP BY, HAVING, and ORDER BY. These commands are the basis of a powerful set of skills for entry-level jobs in data analysis or databases.
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20 Oct 2020
Adrian Więch

What Is a DBMS?

We generate vast quantities of data every day, and that data needs to be stored somehow. That’s where DBMSs come in handy. Find out what they are and how they relate to databases. If you go on a diet and simply want to keep track of your weight, you can probably use a piece of paper and a pencil. If you then want to chart your daily caloric intake, you’ll probably switch to something like a computer spreadsheet.
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16 Oct 2020
Adrian Więch

Google Analytics and SQL

Google Analytics is a very popular tool among website and blog owners alike. With a simple and quick setup, it lets you gather data about your web page visitors easily. However, did you know that you can export data from Google Analytics to create your own SQL reports? Read this article to find out how. Google Analytics is an extremely popular and powerful solution that lets you collect and analyze various kinds of information about your website.
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13 Oct 2020
Martyna Sławińska

What Is a Self Join in SQL? Explaned With 7 Examples

The self join is a popular special case of the SQL JOIN. While most JOINs link two or more tables with each other to present their data together, a self join links a table to itself. This is usually done by joining a table to itself just once within a SQL query, but it is possible to do so multiple times within the same query. Typically, each table in a database stores a specific type of information.
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9 Oct 2020
Marija Ilic

How to Join the Same Table Twice

JOIN is one of the most common statements in SQL. As you may know, it is used to join and combine data from two or more tables into one common data set. In this article, I’m going to discuss special types of joins? in which you combine the same table twice—including joining a table to itself, also known as the self join. When and why do you need to do this?
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8 Oct 2020
Marcin Koryszewski

5 Best Online SQL Courses for Business Analysts

Why bother to learn via an online SQL course? SQL is pure profit – it allows analysts to interpret data efficiently and companies to adopt better strategies. In this post, we’ll look at our top 5 SQL courses for business analysts. Being into finance, economics, and IT systems has brought you to business analysis. It’s a fascinating combination of skills; you’re combining business and technology, which makes you a valuable asset to your company.
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