Sql Basics

Ignacio L. Bisso

The SQL EXISTS Operator

Using the SQL EXISTS clause allows us to create complex queries in a simple way. Learn the pros and cons of the EXISTS operator in this article. In SQL, the EXISTS operator helps us create logical conditions in our queries. Essentially, it checks if there are any rows in a subquery. We’ll show you EXISTS syntax, provide some usage examples, and then give you several exercises to practice on.

Maria Durkin

The SQL BETWEEN Operator

SQL comparison operators are essential tools for filtering data in database queries. Among these operators, the BETWEEN operator stands out as an important tool for specifying ranges inside datasets. SQL comparison operators, such as BETWEEN, are useful for filtering data in database queries. The BETWEEN operator allows you to select rows within a given range, making it ideal for tasks like segmenting an audience by age ranges, identifying thresholds for items between certain quantities, or categorizing performance based on exam scores.

Jill Thornhill

The SQL MIN() Function

SQL has a variety of powerful aggregate tools, including the SQL MIN() function. This article is a quick reference guide to extracting and using minimum values in your queries. In today’s cutthroat business environment, it’s vital to be able to analyze your organization’s data effectively to make informed decisions. SQL’s aggregate functions let you carry out all kinds of statistical analysis on your data. This article is a reference guide to the SQL MIN() function, which extracts the smallest item from a column of data.

Kamila Ostrowska

Top 5 SQL Tutorials for Beginners

Is learning SQL with tutorials a good idea? What tutorials are tailored to your needs? Our top 5 SQL tutorials for beginners will help you find your way! The idea to learn SQL is one of the best you could have. But to succeed, you need a good source of knowledge. In this article, we focus on online tutorials. We will describe different platforms, methods used, key features, prices. After reading this, you’ll be able to choose the best beginner-level SQL tutorial for you.

Jakub Romanowski

The Best Online SQL Editors

When it comes to online SQL editors, you have lots of options. Find out what features you should look for and what editors we prefer in this article. In this article, I'm going to share my insights on online SQL editors. These handy web-based tools have made my SQL query execution and database management tasks much simpler and more accessible – especially when compared to traditional desktop software. I'll discuss their key features and offer guidance on choosing the right one for different needs, whether you're a beginner or an experienced user.

Tihomir Babic

Basic SQL Query Practice Online: 20 Exercises for Beginners

These 20 exercises are just what beginners need for SQL query practice. Try to solve each of them, and then look at the solutions. If something needs to be clarified, there are explanations for each solution. In this article, there’ll be less talking than usual. Instead, you’re going to write the answers to SQL practice queries. (Don’t worry; we’ve included the solutions if you get stuck.) The whole point is to give you, as a beginner, plenty of opportunities for SQL query practice.

Valentyn Kucherenko

An SQL Basics Primer for Non-IT Professionals

You don’t need to be an IT professional to understand SQL. Our quick primer of SQL basics is perfect for beginners without any computer science or programming background. If you’ve ever tried to learn a new software program, you know it takes more than just a few minutes. But it doesn’t mean you can’t learn it! The same is true if you want to learn SQL and databases. Even if you don’t have an IT background, you can do it.

Kamila Ostrowska

How to Learn SQL Without Any Programming Knowledge

If you think that learning SQL is only for programmers, you are deeply wrong. This skill is totally within your grasp! SQL is not just popular and in demand; it’s also quite easy and intuitive to learn. Read on to find out more! You’re searching for inspiration on how to start learning SQL. Maybe you want to change your job, or want to become more competitive in the job market.

Dmitri Vaitkun

The Most Important SQL Commands

In this article, we'll explore the most common SQL commands that everyone should know, including SELECT, INSERT, WHERE and more. We’ll also give examples of how to use each command. Are you ready to dive into the world of databases? SQL, or Structured Query Language, is a programming language that is designed specifically to interact with databases. It allows you to manipulate the data in databases in multiple ways – e.

Kamila Ostrowska

How to Learn SQL

It takes quite an effort to learn SQL or any new skill for that matter. But pushing hard is not enough to learn it successfully. You can sit for hours and still feel like you're not making progress. So, what do you do? Let it go or try even harder? I say: work smart, not hard. SQL (Structured Query Language) is one of the most popular programming languages. It is an invaluable tool in a world overflowing with data.

Kamila Ostrowska

5 Tips for Learning SQL for Beginners

Being data-driven is a hot trend right now. Employers are looking for people who can work with databases. This is why you should learn SQL. In this article, I'll explain how to go about doing so. Yes, learning SQL may be the right thing for you even if you have never seen a line of code. As with any new skill, it requires the right approach and the right resources.

Kateryna Koidan

Will SQL Ever Be Replaced?

Is it worth learning SQL? Is it possible that one of the modern programming languages or no-code solutions will replace SQL very soon? No; it is not that easy to replace SQL and relational databases. Let’s see why SQL is future proof – and why learning it will pay off for many years to come. If you are building your career in a data-driven company, you are probably looking into opportunities to enhance your skill set in data management and data analysis.

Jakub Romanowski

Top 5 SQL Audiobooks

No time to learn SQL? What if I said you could learn while sitting in traffic or washing dishes? It’s possible thanks to SQL Audiobooks. Check out which ones you should listen to. I have been recommending various SQL books for a long time. If selected well, they can be a great complement to the knowledge gained in interactive online courses. If you haven't read my article yet, check it out.

Adrian Więch

How To Learn The SELECT Statement in SQL

When you think about learning SQL, one of the first things you come across is the SELECT statement. Selecting information is arguably the most important SQL feature. In this article, we’ll demonstrate the typical use cases for SQL SELECT with practical examples. Read this article if you’re a beginner database user and would like to know what SELECT can do for you. SQL, or Structured Query Language, is the programming language the IT world uses to communicate with databases.

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.

Adrian Więch

What Is a DBMS?

Updated on: February 19, 2024 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.

Jakub Romanowski

How to Learn SQL Fast

Updated on 11th Oct 2023. Are you in a rush to boost your data analysis capabilities? Dive into our comprehensive guide and learn SQL fast! You work with data every day, but you've had enough of how long it takes to process your giant table in Excel. The time has come for a much better tool: SQL! But how long does it take to learn SQL? In this article, I'll show you how to learn SQL fast and become the Vin Diesel of data – how to become the "

Jakub Romanowski

Top 10 Laptops for Learning SQL in 2020

If you want to learn SQL, you’re going to need a device that’s portable and powerful. I recommend a laptop. Here are the features you’ll need, as well as my picks for laptops to get you learning SQL in 2020! I must admit that browsing Amazon’s computer offers or entering any computer store can give you a headache. So many models, with so many options! They differ in components, workmanship, battery life, and screen size and resolution.

Agnieszka Kozubek-Krycuń

What Is a SQL Dialect, and Which one Should You Learn?

Updated on: September 12, 2023 SQL, standard SQL, SQL Server, MySQL, PostgreSQL, Oracle, … You’d like to learn SQL, but you feel overwhelmed with options and you don’t know where to start. We’ll explain what each of these terms mean and what this has to do with SQL dialects. Diving into the world of SQL dialects can feel like jumping into a deep pool without knowing how to swim. There's a ton of stuff to pick up!

Rebecca McKeown

Why Learn SQL for iOS and Android Development?

App and program development with iOS and Android is a huge and rapidly growing field in the software world. While some developers get through their careers knowing only their chosen development language, there are plenty of reasons to add SQL to that skill set. Here at LearnSQL.com, we are often asked: “why Learn SQL for iOS and Android development?” To answer that question, we’ve put together a little explanation about exactly why learning SQL makes sense for those in the app development space.

Marcin Koryszewski

Listen to These 7 SQL Podcasts

Are you learning SQL online but craving more? If you're looking for a way to squeeze some sweet SQL knowledge into your day, try listening to a SQL podcast. Choose one of our picks and get ready to amp up your SQL game! If you're like me, you like to get deep into a topic. You’re practicing it whenever there’s an opportunity. Of course, It’s hard to make time. I cherish the days I’m able to sit down and just get some hands-on learning done.

Kate Stolarek

How to Learn the SQL Syntax

Updated on: June 26, 2024 Understanding the basic SQL syntax is crucial for learning SQL. Read about what SQL is, and choose the best way for you among a wide variety of possibilities for learning SQL and remembering its syntax. Learning SQL can be a bit tricky, even if people say it's an easy language, especially when it comes to its syntax. Getting the hang of basic SQL syntax is key for learning SQL, and with so many ways to learn, it's vital to pick the one that fits your style best.

Rebecca McKeown

Is it Difficult to Learn SQL?

It’s the number one question asked by the students of SQL and those new to the IT world. Is it difficult to learn SQL? If you came here because you’ve been pondering that very same question, take some comfort in the fact that in no way are you alone. Even the idea of SQL can be intimidating to those of us without a tech background, but it doesn’t have to be that way.

Agnieszka Kozubek-Krycuń

How to Get the First Day of the Week in SQL Server

This is additional content for the LearnSQL.com course Customer Behavior Analysis in SQL Server. This interactive course will teach you how to analyze customer lifecycle in a SQL database in over 70 hands-on exercises. You will learn how to find out compare registration rates between periods of time, compute conversion rates in SQL, compare customer cohorts, analyze customer activity and customer churn over time. This course is essential for anyone doing customer analysis in their job.

LearnSQL.com Team

Stay at Home and Learn SQL for Free with LearnSQL.com

Working remotely is a dream come true for some. You ditch commuting and have more time for the people you love and the things you enjoy. For others, it's a challenge to maintain their focus when there are new distractions. It's also an opportunity to invest the few gained hours in learning something new. Staying at home can be a time when you might find yourself busier than you've ever been, but not getting many things done, and worse, not learning what you planned to.

Shanika Wickramasinghe

Difference between GROUP BY and ORDER BY in Simple Words

For someone who is learning SQL, one of the most common places to get stuck is when learning the GROUP BY command. GROUP BY and ORDER BY are two important keywords in SQL that we use to organize data. The difference between GROUP BY and ORDER BY is that ORDER BY is more simple than GROUP BY and is usually introduced early in an SQL course. Sometimes, people are quite confused over these two concepts (SQL ORDER BY vs.

Jakub Romanowski

Join us on Facebook–We Can Learn More Together

We are so happy that you have joined us to learn and develop your SQL skills! We want to invite you to a new Facebook group, We Learn SQL. It is a great place for anyone interested in meeting like-minded people who also want to learn about database-related concepts. Learning together is easier, don't you think? Joining this group is a great opportunity to begin sharing your learning experiences with others.

Belma Mesihovic

Grouping Data in SQL Server

People who work with data know that data grouping can sometimes be a chore. If you struggle and waste hours with Excel, OpenOffice, or some other tool trying to group various sets of data, take a look at this article and learn how to do the work much quicker and easier by using SQL. You often find yourself in a situation where you need to analyze data and present the results in a form other than the one in which the data is stored.

Ignacio L. Bisso

SQL Order of Operations

SQL is not a traditional programming language in which you write a sequence of instructions in a given order of execution. Instead, SQL is a "declarative" language, which means that by writing a SQL query, you declare what data you expect as a result of the query, but you don't indicate how to obtain it. Six Operations to Order: SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY By using examples, we will explain the execution order of the six most common operations or pieces in an SQL query.

Dorota Wdzięczna

The Most Important SQL Queries for Beginners

How do you get data from a table? How do you create or delete a table? How do you display distinct records? How do you select rows which store a specific value in a column? You can easily do all of this by writing basic SQL queries. This guide discusses the 30 most important SQL queries for beginners. Let's take a look. 1. Retrieving Data From All Columns This is a very basic query to display all data from a table.

Jakub Romanowski

YouTube Tutorials That Actually Teach You Some SQL

YouTube is not just funny cats, music clips, and viral videos. It can also be a mine of knowledge – if you know where to look. Can YouTube tutorials really help you learn SQL? Let's say you're a marketer or an accountant. You work with databases every day. But when it’s time to write a query and get specific data, you need to call someone from IT. Why not learn to do it yourself?

Dorota Wdzięczna

24 Rules to the SQL Formatting Standard

Writing queries to a database requires knowledge about SQL syntax, but this is not all you should know. Best practices for writing professional SQL code require good formatting skills. In this article I discuss why this is so important and what are the basic rules you should follow. Why is it Worthwhile to Format SQL Code? Beginner SQL programmers often don't pay much attention to formatting their code. If you think formatting is something that can be safely ignored, look at the code below:

Ignacio L. Bisso

SQL INNER JOIN Explained in Simple Words

In this article, I will cover perhaps the most important element of the SQL language. That's right! I'm talking about the SQL INNER JOIN clause. As you know, in a database the data are stored in several tables. In my last article, I covered how to create SQL queries when the data you need is in only one table. But what if the data you need is in two tables?

Adrian Więch

Forget About Excel, High Five With SQL

Updated on: May 4, 2024 Find out why you should forget about Excel and start using SQL even if you’re not an IT expert. We’ll show you how easy it is to learn SQL, how it can make you work better, and how LearnSQL.com makes the learning process fun. “I Don’t Deal With Data” We frequently hear the sentence above from people outside the IT industry. Well, it’s not entirely true.

Dorota Wdzięczna

14 Differences Between Standard SQL and Transact-SQL

In my last article, I roughly described how standard SQL differs from T-SQL and who should learn which. Now I'd like to focus on the syntax differences and illustrate these differences with examples. If you think T-SQL is an extension implementing all the features from standard SQL, you aren't right. However, in SQL Server you will find almost all the features of the SQL standard. In this article you will find examples of some of the differences in syntax between standard SQL and Transact-SQL.

Dorota Wdzięczna

What's the Difference Between SQL and T-SQL?

If you are beginning to learn SQL and are confused by the differences between standard SQL and other similar languages like T-SQL, this article will help make things clear. You’ll not only learn about the difference between SQL and T-SQL but also find explanations concerning which topics would be better to start learning first: standard SQL or something more specific like MS SQL Server. What is Standard SQL? SQL (Structured Query Language) is a basic ANSI/ISO standard programming language designed to operate on data stored in relational databases.

Ignacio L. Bisso

Learn SQL on Your Lunch Break

Do you think learning SQL will help you in your career? You are right. SQL is one of the easiest computer languages to learn. These days many non-IT employees have SQL skills and use them to extend their professional capacity. Moreover, more and more companies are encouraging their employees in non-IT areas (like sales, advertising, and finances) to learn and use SQL. One of the benefits of empowering employees with SQL skills is that once you answer one data question, the results will generate a new data question, and then perhaps a cascade of further data questions.

Roman Pijacek

Microsoft SQL Server Pros and Cons

Thinking about using Microsoft SQL Server? If so, you’re in the right place. In this article, we’ll go over the pros and cons of Microsoft SQL Server and evaluate the platform from both a company’s and a data specialist’s perspective. What Is Microsoft SQL Server? Before diving into the pros and cons of Microsoft SQL Server, I’ll explain what it is. In technical terms, it is a relational database management system (RDBMS) developed by Microsoft.

LearnSQL.com Team

Practical Ways to Improve the Performance of SQL Queries

Knowing how to improve SQL query performance is an important skill, especially when working with with large databases. In this article, you'll learn how to write more efficient SQL queries to get results faster. The biggest difference between SQL and other languages is that SQL is a non-procedural language. In a non-procedural language you specify the results that you need but not the methods used to get it. The advantage of a non-procedural language is that it is easier to write programs, therefore it is common for non-programmer business users to generate reports from SQL queries.

Aldo Zelen

How SQL supports data-driven organization

Typical business users make decisions based on gut feelings, but this can't get them so far. In this article, we'll look at how learning to write basic SQL queries helps your company become a data-driven organization. Businesses face many decisions. Do we increase our advertising budget in one region or the other? Are certain products selling quickly enough? What we should do if they aren't? Most of these decisions are driven by intuition, but organizations that make the most business impact use data-driven decision-making.

Dorota Wdzięczna

Microsoft SQL Server 2017 Installation Step by Step

Microsoft SQL Server is one of the most popular professional database servers on the market. In this guide, I’ll show you all SQL Server 2017 installation steps to help you install it on the Windows operating system together with SQL Management Studio. If you want to learn T-SQL, the dialect of SQL used in SQL Server, check out our SQL from A to Z in MS SQL Server track.

Ignacio L. Bisso

How to Begin Running SQL Queries

In this article, I’ll explain how to run a SQL query to help you execute your first one. Let’s jump right in! Running SQL queries for the first time is not a complex task, but it can seem intimidating at first if you’re a complete beginner. But once you get past that initial roadblock, you’ll be able to focus on learning SQL and writing more interesting queries to meet your business needs.

Aldo Zelen

SQL Indexing 101

Indexes are one of the most misused and misunderstood entities in physical database design. A good understanding of indexes and how they solve database performance problems is necessary for any database novice. In this article, we'll look at basic database indexes and their role in database development. To picture what an index is, consider a textbook. At the end of most textbooks is an index listing all the terms one can find in the text and the pages on which they appear.

Aldo Zelen

How to Use a SQL Wildcard

SQL wildcard allows us to filter data matching certain patterns in SQL. We use SQL wildcards with the LIKE operator in the WHERE clause of a query to filter data. In this beginner’s article, we’ll look at everything you need to know about basic SQL wildcards. If you like playing cards, then you know that wildcards can substitute any other card in your deck. Similarly, SQL wildcards can substitute one or more characters.

Aldo Zelen

SQL Filtering 101

Sometimes, SQL queries return lots of data you don't need. In this article, we'll look at a simple example of filtering SQL queries to reduce the complexity of your data. The key to learning how to filter data in SQL is understanding the very basics of Boolean algebra. That's just a fancy term mathematicians use to describe expressions involving logical values (true/false) and their associated operators (and, or, not, etc.

Kate Stolarek

Why Learn SQL Over the Summer

Think summer is reserved for flying to warm places and hanging out at the beach? Sure! But it's also a great time to learn new skills that you haven't had time for. If you recently graduated from high school and want to get a head start on computer programming for college, learning SQL over the summer is a great opportunity. You have nothing to lose and everything to gain—SQL is actually really easy to learn, especially with so much free time over the summer.

Ignacio L. Bisso

Improving Slow Query Performance: When Runtime Matters

As SQL users, we usually focus on writing queries that return correct results. However, there are more things to consider when you're writing a query; one of them is query performance. In this article, we'll look at some examples where query response time is critical. Scene One: 911 Call Center Let's suppose we're at a 911 call center, when the phone rings. One of the operators answers the call; a witness reports that a man has been shot.

Ignacio L. Bisso

Converting Subqueries to Joins

Not all queries are alike, especially in terms of performance. In this article, we'll look at how you can convert SQL subqueries to joins for improved efficiency. When should I use SQL subqueries? Great question! Unfortunately, there's no concrete answer. SQL beginners tend to overuse subqueries. Typically, once they find that SQL construction works in one situation, they try to apply that same approach to other situations. It's only natural.

Aldo Zelen

Essential SQL Terms to Know for Beginners and Pros

Updated on: April 11, 2024 Working with databases can seem daunting to a non-technical person. Right away, you’re bombarded with new terms that make your head spin. Database, database instance, table, SQL and others are some of the basic terms that you need to understand just to have a normal conversation with your technical colleagues. In this article, we’ll explore some basic SQL database terminology you need to know to succeed.

Ignacio L. Bisso

Learn to Write a SQL Correlated Subquery in 5 Minutes

If you’re familiar with the famous Russian nesting doll, then SQL correlated subqueries should be a peace of cake to understand—subqueries are just queries nested within queries. An SQL subquery is often called an “inner” query; the main query is usually called the “outer” query. This article covers everything you need to know about correlated subqueries. What Exactly is a SQL Correlated Subquery? A correlated SQL subquery is just a subquery that is executed many times—once for each record (row) returned by the outer (main) query.

Dorota Wdzięczna

New LearnSQL.com Online Practice: SQL Practice Set

If you’re looking to retrieve any kind of information from a database, you need to speak its language. But querying databases is an art—and it demands practice. That’s why we created our SQL practice set: a pack of SQL online practice exercises meant to help you master your skills. We spend a lot of time not only developing new courses but also speaking with our users and learning what they expect from SQL online practice exercises.

Aldo Zelen

How to Become a Database Analyst

Curious about becoming a database analyst? Maybe you've taken some database courses at university and they really struck a chord. Or maybe you learned online. Now you're thinking about making a career out of working with databases. Where would you start? What should you expect at each phase of your professional development? In this post, we'll explore the challenging and exciting world of databases analysis. We'll go from the very beginning of a career to the apex of professional success.

Jeffrey Edison

How to Start Thinking in SQL

Updated on: June 22, 2024 Thinking in SQL will help you understand what SQL queries do, how to create and change them, and how to create reports from the data you obtain. If you want to know how to write better SQL queries, you have to change the way you think about the code. One of the greatest skills you can have in SQL programming is the ability to change an existing SQL query so you get the results you need.

Ignacio L. Bisso

How to Remove Junk Characters in SQL

Unwanted characters in text data can be a bit of a pain, but there’s an easy way to fix them. Scroll down to learn how to remove junk characters in SQL in the easiest way! Sometimes, we’ll find unwanted characters inside our string data because our SQL queries didn’t work as expected. Moreover, these extra characters may sometimes be invisible, which really complicates things. In this article, we’ll examine some string-related SQL functions that can handle unwanted characters—visible or not!

Ignacio L. Bisso

How to Solve Capitalization Data Quality Issues

Misspelled names, typos, and text data quality issues in your database? Power up your queries! Use SQL string functions to address data quality issues related to capitalization. Sometimes, our SQL queries don't work as expected because of data quality issues. In this article, we will examine some string-related SQL functions that can correct data quality issues related to capitalization. We'll be using PostgreSQL in our examples, but similar functions are available in most database engines.

Ignacio L. Bisso

The SQL Coalesce Function: Handling Null Values

You may already know how to return null values in SQL. Now, we’re going to learn how to do the opposite. Though the SQL COALESCE function may seem complex, it’s actually very straightforward and useful. Let’s look at several examples of how the SQL COALESCE function can be used to work with NULL values in SQL. The Need for Coalesce in SQL Before we dive into the SQL COALESCE function in detail, you should understand how NULL values behave in expressions.

Kacper Skawina

Analyzing Survey Data: Explore Results Using SQL

Excel is a powerful beast that lets you analyze complex data. Yet, operating on big chunks of data can sometimes be a daunting task. Let's take a look at how SQL can help. Today, we'll tackle a common problem with importing data to an SQL database, using a real-life example. Suppose your company conducted a survey on the most popular programming trends and preferences, striving to meet the expectations of its users.

Ignacio L. Bisso

SQL Date and Interval Arithmetic: Employee Lateness

Computing Tardiness: Date, Time, and Interval SQL Arithmetic In this article, we’re going to discuss some interesting operations we can perform with date-related data types in SQL. The SQL standard, which most relational databases comply with these days, specifies the date-related data types that must be present in relational databases. The most important of such data types are date, time, timestamp, and interval. Here’s a brief rundown of the differences between these data types:

Dorota Wdzięczna

SQL Hacks To Control Family Budget On Black Friday Weekend

If you’re in the US, chances are you’ve been eagerly awaiting the approach of Black Friday just as much as Thanksgiving. Though the shopping frenzy takes hold of nearly everyone, some people have to stick to their budgets and shop prudently. In this article, we’ll take a look at how generating an SQL report can help you track how much your family spent shopping on Black Friday. Storing Black Friday Purchases in a Database Before we can create an SQL report, we first need some data we can use.

Ignacio L. Bisso

SQL Window Functions By Explanation

In our previous post, we explained how SQL window functions work by example. We started with some very simple, basic functions. Let's extend it by explaining subclauses in window functions. SQL window functions are a great way to compute results from a set of rows rather than a single row. As you know from our first article, the "window" in window function refers to the set of rows. We showed you some examples of simple window functions like RANK and LEAD.

Aldo Zelen

Long SQL Query vs. Recursive SQL Query

Recursion is one of the central ideas in computer science. We can define it as a method for solving problems where the solution of the problem depends on solving a smaller instance of a problem. If this sounds complicated do not fret, in this article we will learn about recursion in SQL that you can practice and deepen at LearnSQL.com. Recursion is a way of solving hierarchical problems we find in data with common SQL.

Dorota Wdzięczna

An Illustrated Guide to Multiple Join

So far, our articles in the "An Illustrated Guide" series have explained several join types: INNER JOINs, OUTER JOINs (LEFT JOIN, RIGHT JOIN, FULL JOIN), CROSS JOIN, self-join and non-equi join. In this final article of the series, we show you how to create SQL queries that match data from multiple tables using one or more join types. Join Types in SQL Queries Before we start discussing example SQL queries that use multiple join types, let's do a short recap of the join types we've covered so far, just to be sure you understand the differences.

Dorota Wdzięczna

An Illustrated Guide to the SQL Non Equi Join

Did you know that in SQL, a join doesn’t have to be based on identical matches? In this post, we look at the SQL non equi join, which uses ‘non-equal’ operators to match records. We’ve already discussed several types of joins, including self joins and CROSS JOIN, INNER JOIN and OUTER JOIN. These types of joins typically appear with the equals sign (=). However, some joins use conditions other than the equals (=) sign.

Dorota Wdzięczna

An Illustrated Guide to the SQL Self Join

What is an SQL self join and how does it work? When should it be used? We’ll provide answers to those questions! In SQL, we can combine data from multiple tables by using a JOIN operator. JOIN has several variants; we’ve already discussed CROSS JOIN, INNER JOIN, and OUTER JOIN. Most of the time, these operators join data from two or more different tables. You can practice all the different types of JOINs in our interactive SQL JOINs course.

Marija Ilic

How to Track Down Duplicate Values in a Table

When it comes to information management, duplicates present one of the most common challenges to data quality. In this article, I'll explain how it is possible to find and distinguish duplicate names with the help of the SQL data programming language. I really like my maiden name. The reason I like it so much is because it's rare. My maiden name (first with last) provided a unique identifier on platforms such as LinkedIn, Facebook, Twitter and similar.

Jenny Hung

Four Reasons You Must Learn SQL in Data Science

Is SQL important for data science? It certainly is! This language can help you build a foundation for your analytical career. Let’s see how you use SQL in data science. Data science is hot right now. What if you could predict the next market crash? Or contain the spread of Ebola? Or accurately predict a health crisis months or even years before it happens? Data scientists are working hard on these kinds of projects, and they are earning healthy salaries in the process.

Kamila Ostrowska

5 Reasons Why No One Should Be Afraid to Learn SQL

Updated on: September 17, 2023 Think SQL is just for tech experts? Think again. In this article, we'll bust some common myths and show you that anyone can learn SQL. Let's dive in and make SQL simple. In today’s world, even those in non-technical jobs need some technical skills. And you don’t have to be a hard-core nerd to get these skills. Everywhere you look, from marketing to management, a touch of tech knowledge can set you apart.

Francisco Claria

Referential Constraints and Foreign Keys in MySQL

Foreign keys and referential constraints allow you to set relationships between tables and modify some of the database engine’s actions. This beginner’s guide explains referential integrity and foreign key use in MySQL. One of the most important aspects of database usage is being able to trust the information you store. Database engines provide several features that help you maintain the quality of your data, like defining required columns as NOT NULL and setting an exact data type for each column.

Dorota Wdzięczna

An Illustrated Guide to the SQL OUTER JOIN

We’ve already discussed the SQL CROSS JOIN and INNER JOIN statements. It’s time to explore another: OUTER JOIN. What is it? How does it work? Let’s find out! If you’ve read our other posts, you know that you can link the data in two or more database tables using one of the many types of SQL join operator. Today, we’ll discuss the three kinds of OUTER JOIN: LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL OUTER JOIN.

Dorota Wdzięczna

An Illustrated Guide to the SQL INNER JOIN

What is an SQL INNER JOIN, and how does it work? Let's find out! In my last article, I discussed the CROSS JOIN operation in SQL. Today, we'll look at INNER JOIN and how to use it. Is it the same as a JOIN? How many tables can you link with an INNER JOIN? These are all good questions. Let's look at the answers! What is an INNER JOIN?

Francisco Claria

An Introduction to Using SQL Aggregate Functions with JOINs

Previously, we've discussed the use of SQL aggregate functions with the GROUP BY statement. Regular readers of the our blog will also remember our recent tutorial about JOINs. If you're a bit rusty on either subject, I encourage you to review them before continuing this article. That's because we will dig further into aggregate functions by pairing them with JOINs. This duo unleashes the full possibilities of SQL aggregate functions and allows us to perform computations on multiple tables in a single query.

Marek Pankowski

SQL Set Operators: Union, Union All, Minus, Intersect

Ever heard terms such as union and intersection in SQL? They're examples of set operators, and they come in handy when you need to combine information from multiple tables or queries. In this article, we'll take a closer look at them. SQL queries let us choose the most important bits from large amounts of information. Of course, we can't expect that all necessary data will be stored in one table.

Francisco Claria

Learning JOINs With Real World SQL Examples

The JOIN statement lets you work with data stored in multiple tables. In this article, I’ll walk you through the topic of JOIN clauses using real world SQL examples. Imagine if you could only work with one database table at a time. Fortunately, this isn’t anything we have to worry about. Once you learn the JOIN statement, you can start linking data together. In this article, I’ll use real world SQL examples that illustrate how we use JOINs, how each type of JOIN works, and when to use each type.

Aldo Zelen

5 Books That Will Grow Your SQL Skills

Updated on: April 18, 2024 Looking to take your database skills up a notch? I've spent some time digging into various resources, and I want to share five advanced SQL books that really stood out. These texts are not just about learning the basics: they're about mastering the intricacies of SQL and truly enhancing your database management prowess. Whether you're troubleshooting complex queries or optimizing performance, these books provide insights that are both practical and transformative.

LearnSQL.com Team

The Complete Beginner’s Guide to SQL Fundamentals

LearnSQL.com is a great place to learn SQL. If you’re a complete beginner, it’s best to have an overview of what SQL is, what a database is, and how they work together. In this article, you’ll find a complete guide to SQL fundamentals. SQL Fundamentals: Database Let’s begin our guide to SQL with basic definitions. You might have already heard that SQL is used with databases. What exactly is a database?

Aldo Zelen

Refine Results with SQL Set Operators

Using UNION, UNION ALL, EXCEPT, and INTERSECT to manage SQL query results. The function of SQL set operators is pretty simple; they allow us to combine results from different SQL queries into one result set. The best way to understand how set operators work is to use visual methods like the Venn diagram. For those of you not familiar with Venn diagrams, they are two circles that represent items or collections of items.