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SQL Course of the Month – SQL JOINs

If you want to really learn SQL, you can’t skip SQL JOINs. They are some of the most fundamental and commonly used features of the SQL language. That’s why SQL JOINs is our February SQL Course of the Month. What makes SQL JOINs so important? I asked Agnieszka Kozubek-Krycuń, Vertabelo's Chief Content Officer, about it. Here's what she said.

SQL JOINs Interactive Course

Is it true that SQL JOINs are one of the foundations of SQL?

Yes, that’s definitely true. In SQL, the JOIN operator is used to combine data from two or more tables. Data in databases is usually stored in many different tables, and you often want to combine information from these tables. So, knowledge of JOIN is essential for anyone who wants to work with SQL in real life.

JOIN is a topic that many beginners fear. It’s not really difficult, but it’s usually the first SQL feature people encounter that’s not straightforward to learn. Learners often need some time to practice JOINs and become familiar with them. That’s why it’s important to learn and review JOIN using an interactive course or a similar method that lets you consolidate your knowledge and gain confidence in your skills.

If you want to know more about SQL JOINs, I encourage you to watch the clips on our YouTube channel We Learn SQL. Adrian explains everything in a very simple and understandable way. And remember to subscribe!

Can you show me an example of using SQL JOIN?

Of course. I am a big cinema fan, so my example will be about movies. Imagine that we have a movie table:

idtitleproduction_yeardirector_id
1Psycho19601
2Midnight in Paris20112
3Sweet and Lowdown19932
4Talk to Her20023
5The Skin I Live In20113

Another table, director, contains information about movie directors:

idnamebirth_year
1Alfred Hitchcock1899
2Woody Allen1935
3Pedro Almodóvar1949
If you’d like to see the details of each movie together with the details of its director, you have to use JOIN, like so:
SELECT *  
FROM movie  
JOIN director  
ON movie.director_id=director.id;

We even have a handy animation to show how JOIN works:

How JOIN works

But can't I just work on one table? Will SQL JOINs be useful in this case?

You can, but it’s very rare to only work with one table in real life. A typical database contains many different tables and you often need to combine data from multiple tables.

In the rare instance that you only work with one table, you may still need to join the table with itself. So even if you work with one table, knowledge of JOINs may come in handy.

How long will it take me to do this SQL course? How many exercises are there? What will I learn?

There are 93 interactive exercises in this course. We estimate that it takes about 10 hours to complete them all.

This is a SQL practice course. We assume that the user knows the basics of JOIN and would like to practice writing queries with JOINs. So, we start by briefly reviewing the JOIN syntax, and then there are exercises to practice various JOINs. We focus on topics that are challenging for beginners: telling left JOIN from LEFT JOIN, writing queries that join multiple tables, and joining a table with itself.

The course gives learners many opportunities to practice writing different kinds of JOINs. After completing the course, they’ll have written over 80 different JOIN queries. This gives them confidence in their new skills.

SQL courses at LearnSQL.com combine theory with a lot of practice. Is that also the case here?

Virtually all studies have shown that knowledge is consolidated only when it is applied in practice. We do this in our SQL courses, including SQL JOINs. With each exercise, you will get some theory first and then a task to be solved in our online console. You will be writing real SQL queries. Don't be afraid that you will not be able to cope; if necessary, we are here and we can help.

Is this free SQL course part of a larger track?

SQL ptactice

SQL JOINs course is part of our SQL Practice track. This is one of the best places to practice your SQL knowledge. We strongly believe that practice makes perfect, so you will find over 180 interactive SQL exercises in this track.

Are you preparing for a job interview or exam? Practice it all with our SQL Practice Set. Find out what you need to repeat and what you can be sure of. This last course was our SQL Course of the Month in June 2020.

Who should take this course?

Anyone who is looking to practice their JOINs! It’s perfect for beginners who still feel uneasy about JOIN and would like to build their knowledge. It’s also a good review course for students preparing for an SQL exam or anyone who’s preparing for a SQL job interview.

Will I receive a certificate to post on my LinkedIn profile?

Yes – we do this with all our courses at LearnSQL.com. You will receive a personal PDF certificate that you can download or add to your LinkedIn profile. See how easy it is by reading our guide.

Do you remember working on this course?

After preparing courses in the SQL from A to Z track – which covers all the SQL that you need in daily practice – we thought: What courses do our users need? Our answer was: Users need SQL practice! After completing SQL Basics course, which contains 129 interactive exercises, they still may feel the need to practice some more. And SQL JOINs are a challenging topic that needs a lot of practice. So we prepared this course.

Free SQL Course for February 2021: SQL JOINs

And now for the coolest part:

Throughout February, our SQL JOINS course will be available to everyone for FREE! That’s right – you don't have to pay anything to learn the ins and outs of SQL JOINs. Pretty sweet, right?  All you need to do is sign up for LearnSQL.com and start learning! Take the next step towards success!

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