Articles Cookbook
20 May 2021
Martyna Sławińska

What’s the Difference Between UNIQUE and DISTINCT in SQL?

We use the words unique and distinct interchangeably in our day-to-day life. However, these words play very different roles in SQL. Let’s find out what is so different about them and how we can use them in SQL. Despite the words unique and distinct being synonyms, they cover very different things in SQL. The UNIQUE keyword in SQL plays the role of a database constraint; it ensures there are no duplicate values stored in a particular column or a set of columns.
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19 May 2021
Tihomir Babic

What Is Advanced SQL?

Are you confused about advanced SQL skills? What are they? This article will explain what advanced SQL can mean, especially as we use it on LearnSQL.com. I’m sure you find the phrases ‘advanced SQL skills’ or ‘advanced SQL topics’ very often. You read one article about advanced SQL and you’re happy with how easy these advanced topics seem to be. Then you talk to someone and you see they consider everything you know as basic SQL knowledge.
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18 May 2021
Andrew Bone

How to Use Aliases in SQL Queries

An SQL alias is useful for simplifying your queries and making the query and its result more readable. This article explains why and how you can use aliases in your SQL queries. You can temporarily rename a table or a column by giving it another name. This is known as an SQL alias. It’s a temporary change that does not affect the actual table name in the database. A temporary table name can also be called a correlation name.
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14 May 2021
James Wondrasek

How to Use Comparison Operators with NULLs in SQL

The SQL NULL value serves a special purpose. It also comes with counterintuitive behaviors that can trip up SQL beginners or even experienced programmers. Learn how to avoid these problems when you use NULL with comparison operators. This article is going to help you master best practices for crafting SQL queries that work with NULL values and use comparison operators ( =, <>, <, > ) – which, if you have written any SQL queries before, you know is just about every query you will ever write!
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13 May 2021
Kateryna Koidan

A Detailed Guide to SQL ORDER BY

It’s often necessary to display the output of SQL query in specific order rather than arbitrarily. In this article, I’ll explain the many ways you can do it with the SQL ORDER BY clause. To sort records in SQL, you’ll need to use the ORDER BY clause.  In this article, I’ll explain in detail how to use ORDER BY to sort output by one or more columns, in ascending (A-Z) or descending (Z-A) order, and by using existing column(s) or using column(s) calculated by an aggregate function.
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12 May 2021
Kamila Ostrowska

The Best Books for Data Engineers

Getting tired of the endless screen glare? It might be a good time to switch to a book. Dive into our selected list of books for data engineers, perfect for expanding your insights on databases. It’s a refreshing change from the digital routine! Last time, I shared a list of the best books to learn SQL. This time, I want to introduce a few books for data engineers. They are worth reading and will help you learn more about databases.
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7 May 2021
Zahin Rahman

What Is the WITH Clause in SQL?

In this article, you will learn about the SQL WITH clause, also known as common table expression (CTE). We will go over some examples to demonstrate some of their use cases in light of their benefits. Today, I'm here to guide you through the intricacies of the SQL WITH clause, commonly known as Common Table Expression (CTE). If you've faced challenges with lengthy and complex SQL queries, this article will be particularly useful.
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6 May 2021
Jakub Romanowski

Want to Work With Data? Learn SQL!

Are you looking for a database job? How are things working out? If you don't know what to do, I suggest you start by learning SQL. Here’s why. In this article, I’ll explain how you can succeed at finding a database job. If you are tired of your current job and fed up with your boss (who hasn't given you a raise in years), read on. Stay with me too if one more stupid Zoom call will make you scream.
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5 May 2021
Kateryna Koidan

A Guide to SQL Common Table Expressions

Common table expressions are a relatively new SQL feature that is sometimes overlooked by experienced practitioners working with relational databases. Don’t be one of them! Learn how to use SQL CTEs and join the many data analysts enjoying the benefits of this great tool. Common table expressions (CTEs), also known as WITH clauses, are used to create named subqueries that can be referenced in the main query. CTEs are not saved for future use and can be referenced only within the query where they are defined.
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4 May 2021
LearnSQL.com Team

Course of the Month: SQL Practice Set

Are you starting your adventure with SQL and looking for a place to practice your SQL queries? Or maybe you are preparing for a job interview? I have good news for you. Throughout May, you will have access to our amazing SQL practice course for FREE! Why is LearnSQL.com giving you a free SQL course? Every month, our users get the opportunity to take one of our great SQL courses for free.
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