Back to articles list April 22, 2021 - 9 minutes read Training SQL JOINs Doesn't Have To Be Difficult Tihomir Babic Tihomir is a financial and data analyst turned database designer from Zagreb, Croatia. He has extensive experience in the financial services industry, which helps him combine his finance background with his interest in data. When not tinkering with data, he likes to play the guitar in a band and pretend to be a musician. He also regularly writes columns for the Croatian LGBT news site CroL.hr and hopes to soon write his first novel. Tags: sql learn sql sql joins How can you train your SQL JOIN skills? And where can you do this? Also, why should you even learn SQL JOINs in the first place? All of these questions will soon be answered. One of the positive sides of the internet era is information abundance. One of the negative sides of the internet era is, well, information abundance. The amount of information and knowledge available can be overwhelming. It can be difficult to choose from too much information. What should I read, what should I watch, how do I approach this, and what is the best option? You might end up spending more time trying to make decisions than actually learning. Since you’re here, you’re probably having trouble deciding whether to learn about SQL JOINs. If you have decided you want to, you might not be sure how. I’ll do my best to help you make a good decision. You can’t (or shouldn’t) choose something before you know what it is. That’s why I’ll start with solving the mystery of what SQL JOINs are. What Are SQL JOINs? The SQL JOIN clause is used to get data from two or more tables. This is called joining, hence the JOIN keyword. Tables are joined based on a column that they have in common. Now that you’ve learned what JOINs are, you might be wondering why you should know how to join tables. Let me ask you something. Do you want to work with databases? Yes? That’s why! When working with databases, knowing how to join tables is an essential skill. Joining tables is u-n-a-v-o-i-d-a-b-l-e! Why’s that? The need to join tables is embedded in the concept of databases. The point of databases is to have as much data as possible that is available as fast as possible. One might say these are opposite goals. However, they’re achievable with databases! Data shouldn’t be crammed in one big table. Instead, data in databases are usually placed in several different tables. The only way to get data is by joining these tables. This is done using the JOIN clause, as you learned. So, every time you need data from more than one table, you’ll need to use JOIN. Additionally, you might need it for only one table. JOINs can be used to join a table with itself. I won’t lie to you, understanding JOINs can be difficult for beginners. Understanding when to use each type of JOIN causes the most trouble. When training your SQL JOIN skills, it’s important to differentiate between these four JOINs: INNER JOIN LEFT JOIN RIGHT JOIN FULL OUTER JOIN Each of these JOINs has its purpose and can return different results. Which one to use depends on the data you have and the result you want. And the ability to understand your data and choose a suitable JOIN comes with experience. This experience comes with training and making lots of mistakes. This should be the basis for deciding where to train SQL JOINs. Training JOINs Good JOINs training should be detailed, explaining all four types of JOINs and providing a sturdy theoretical understanding of JOINs. It should also provide plenty of examples for you to practice and make mistakes with. Following several simple tips for beginners will help you understand JOINs. I’m guessing you’re wondering about the four JOINs and what they do. Here are all four JOINs explained in detail using helpful drawings. In practice, I probably use the LEFT JOIN most often. So, I recommend dedicating more time to understanding how the LEFT JOIN works. However, don’t neglect the other three JOINs. I didn’t want to bother you with the “fifth Beatle of the JOINs,” the CROSS JOIN. In case you’re interested, here’s an article with information about the CROSS JOIN. Once you understand how to join two tables, the next step is to learn how to join three tables. So, your training should include this too. There will be no limits when it comes to joining tables once you know how to join three tables. Literally! After joining three tables, adding any number of tables above that doesn’t change anything. It’s the same thing. Again, if you’re using SQL, it’s likely you will need this knowledge. So, how can you make learning SQL JOINs less difficult? I recommend using three methods: Training Working on your own projects Training again Understanding JOINs is not always easy. Choosing the proper way to train SQL JOINs will help you learn more easily and effectively. It will also give you well-rounded knowledge, both theoretical and practical. Which Course? You are now at the part of the learning path where you choose which SQL course is for you. You will use this course for learning and training what you’ve learned. The right course depends on various factors, such as your previous SQL knowledge, topics you want to learn, and so on. I’ll guide you through every LearnSQL.com online course that covers SQL JOINs. By the end of the article, you’ll hopefully be able to choose the right course for yourself! SQL Basics If you’re a total SQL rookie, I recommend the SQL Basics course. It will gradually lead you through the basic SQL topics. Along the way, you will learn SQL JOINs. First, you will learn the basics of relational databases. Then, you will train selecting data from one table. Once you become comfortable querying one table, you’ll learn how to query more than one table. This course is not dedicated only to JOINs. It also covers other topics, such as aggregation and grouping, subqueries, and set operations. By completing this course, you’ll be ready to reach a new level with SQL JOINs. SQL JOINs The SQL JOINs course is dedicated exclusively to JOINs, as you can probably tell from its name. The course is intended for anyone with a basic knowledge of JOINs. Here, you’ll build on that knowledge by learning how to join more than two tables and a table with itself. You’ll also learn the non-equi JOINs. As I said, it’s important not only to learn something but also to train what you learned. This course will give you plenty of opportunities for training with 93 interactive exercises. JOINs in MS SQL Server and PostgreSQL JOINs The previously mentioned course will teach you how to write queries in standard SQL. However, if you’re using MS SQL Server or PostgreSQL, you might want to learn and train JOINs in one of those two dialects. It can be confusing to switch between two different dialects: one for learning and one for work. To avoid this, you can choose between the T-SQL and PostgreSQL dialects. Both the JOINs in MS SQL Server course and PostgreSQL JOINs course offer you 93 interactive exercises for honing your skills. SQL Practice Track and SQL Practice in PostgreSQL Track Our practice tracks are specially designed to teach you SQL skills and to review and consolidate your knowledge. Both the SQL Practice Track and SQL Practice in PostgreSQL Track contain the SQL JOINs course and the SQL practice set. By choosing either track, you’ll review topics such as SELECT statements, the WHERE clause, SQL JOINs, SQL subqueries, and aggregation with GROUP BY and HAVING. The only difference is in the dialect. In the SQL Practice Track, you’ll use Standard SQL. If you choose the SQL Practice in PostgreSQL Track, naturally, you’ll use the PostgreSQL dialect. Work on Your Own Projects Once you learn about SQL JOINs and get lots of training in the course’s safe environment, it’s time to use your knowledge and skills in real life. This means working on your own projects. This is essential for several reasons. It will put you in situations that no course can prepare you for entirely. You’ll have to work under a deadline. And you’ll have to deal with actual, imperfect data. This will allow you to build on the knowledge you gained from the courses. You’ll find creative ways to solve problems. You’ll think more quickly and pragmatically. And you’ll sometimes have to dig deep into data and make changes for something to work. You’ll probably need to review how some JOINs work, especially when you start doing your own projects. Don’t worry. That’s perfectly normal. To help you concentrate on solving problems and not JOINs syntax, we created the SQL JOINs Cheat Sheet. You can use it to quickly recap JOIN logic. The syntax is shown in clear examples. You can save it in your browser, download it, or print it out so that you can use it whenever you need it. Train Again Now and then, I recommend training certain topics again. This means returning to a course and going through the topics you’re interested in. By doing this after you’ve finished your own project, you’ll greatly consolidate knowledge. Returning to a course can also be helpful while you’re working on a project. Sometimes, you might do something with your project and not fully understand why. Training again can open your eyes and help you better understand why you did something. It can also give you ideas for how to do something differently, in your current project or future ones. This is all part of the learning curve. Forgetting is also part of the learning curve. If you’re not using what you learned, you’ll probably forget it. Continuing to train is especially important in such cases. So, if you don’t start working on your own projects after training SQL JOINS, you might want to train again. Here is another reason to train again: interviews. Yes, job interviews. If you’re going to an interview for a job that requires SQL knowledge, you’ll most probably be asked about SQL JOINs. As I said, this is fundamental knowledge when working with databases. So, it’s not surprising it often appears in job interviews. The interviewer could, for instance, ask you what JOIN is or to explain different types of JOINs. You could even be asked to write code that joins two or three tables. These are all entry-level questions. If you’re interested in landing a job requiring basic SQL knowledge, you can prepare by reading these eight questions and answers. SQL JOIN questions can also appear in advanced SQL interviews. For instance, how would you filter data using JOIN? Or, what is a non-equi JOIN? Or, how do you join the table with itself? You can find more advanced SQL questions and answers here. Are You Ready To Start Training SQL JOINs? In this article, I did my best to help you decide if learning SQL JOINs is for you. As you just learned, SQL and SQL JOINs are necessary for everyday work with databases. Mastering JOINs will give you more comfort and confidence, and your queries and reports will be more efficient. They will be even more complex and informative. If you decide to learn about SQL JOINs, it’s important to structure your learning. Ideally, combine training, working on your own projects, and training again. You can choose from several great SQL JOIN online courses. After you choose the one for you, you will join the exciting world of SQL JOINs! Tags: sql learn sql sql joins You may also like SQL JOIN Tips for Beginners Four tips for learning and using SQL JOINs. Our examples show you why these should become second nature when joining tables. Read more SQL JOIN Topics That Require Practice Find out which beginner, intermediate, and advanced JOIN topics you should practice. Practical examples will help you grasp various JOIN concepts. Read more SQL JOIN Cheat Sheet This 2-page SQL JOIN Cheat Sheet covers the syntax of different JOINs (even the rare ones!) Download it in PDF or PNG format. Read more SQL JOIN Types Explained Learn how to join tables in SQL. Review the different SQL join types and when to use inner join, left join, right join, or full join. Read more How to Learn SQL JOINs Learn how to use SQL JOINs to effectively combine data across multiple tables and analyze sophisticated data sets. Read more How to Join the Same Table Twice Learn when and why you need to join the same table twice in SQL, including when you should use self joins. 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