Group By

Tihomir Babic

Top 9 SQL GROUP BY Interview Questions

Preparing for an SQL job interview? This guide will walk you through nine basic, intermediate, and advanced GROUP BY questions that you may have to answer. There are common GROUP BY questions that pop up in a lot of SQL job interviews; in this article, we’ll explain how to answer them. If you are a data analyst or another data professional preparing for an interview, this article aims to help you out.

Jakub Romanowski

Free Course of the Month – GROUP BY Extensions in PostgreSQL

Do you work with data? Want to be able to create better and more sophisticated SQL reports? Then check out our interactive GROUP BY Extensions in PostgreSQL course. In April 2022, you can complete this online PostgreSQL course for FREE! How can you get this free SQL course in April? Create a free com account or log in if you already have one. Start the course. You will have free access to its content until the end of the month.

Tihomir Babic

How to Include Zero in a COUNT() Aggregate

Explaining how to include zero (0) counts in your SQL query result. Here’s the problem: you want to count something that doesn’t exist, and you want to show your result as zero. How do you do that in SQL? Using the COUNT() aggregate function is a reasonable first step. It will count all the data it finds and return the number of occurrences. But what if there are no occurrences of certain data?

Andrew Bone

How to Sort Values in a Specific Order in SQL

Sometimes you will be required to order your data in a particular way, and often the use of typical sort modifiers like ASC and DESC are not enough. This article will show you how to use the CASE statement to order your data exactly how you need it to be. Have you ever needed to order your data in a very specific way? One of the best methods for handling complex sorting is using CASE.

Himanshu Kathuria

Who Has the Highest Salary, Department-wise? Use SQL to Find Out!

This article shows how to get the total salary by department for an organization, using the GROUP BY functionality of SQL. We explain the SQL GROUP BY clause in detail along with conditional filtering using a HAVING clause. Understanding the salary outlay for an organization is one of the common starting points for business leaders. It helps them see who in the organization has the highest total salary cost, department-wise.

Andrew Bone

What Is the SQL GROUPING SETS Clause, and How Do You Use it?

GROUPING SETS are groups, or sets, of columns by which rows can be grouped together. Instead of writing multiple queries and combining the results with a UNION, you can simply use GROUPING SETS. GROUPING SETS in SQL can be considered an extension of the GROUP BY clause. It allows you to define multiple grouping sets in the same query. Let’s look at its syntax and how it can be equivalent to a GROUP BY with multiple UNION ALL clauses.

András Novoszáth

What Is the SQL HAVING Clause?

Are you learning SQL? Are you wondering what you can use the HAVING clause for? Or, perhaps, have you tried to use WHERE on your GROUP BY aggregates? You are in the right place! In this article, we explain how to use HAVING with plenty of examples. Have you tried to filter your metrics you created with GROUP BY with a WHERE clause and found out that it did not work?

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.

Jakub Romanowski

Want to Learn GROUP BY Extensions in PostgreSQL? You've Come to the Right Place!

Do you want to take your knowledge of PostgreSQL to the next level? I have something for you: LearnSQL.com’s new GROUP BY Extensions in PostgreSQL course! It will help you get even more out of your data and create better reports and summaries. Fasten your seat belts and prepare to see what GROUP BY can do when it’s turbocharged. First, I have to confess something. I am not objective – I think PostgreSQL is the best and coolest SQL dialect.

Marija Ilic

What Is GROUP BY in SQL?

GROUP BY is a great SQL feature that allows you to perform powerful calculations on grouped data. Do you want to learn how to get powerful insights from your data? Would you like to know what GROUP BY does and when you should use it? If your answer is yes, keep reading. In this article, you will learn exactly that. Why You Need GROUP BY In today's digitized world – no matter what business you are in – database tables are usually huge, with millions of records.

Agnieszka Kozubek-Krycuń

Why Aren’t SQL Window Functions Allowed in GROUP BY?

It’s true – the SQL order of operations means window functions aren’t allowed in GROUP BY. But you can use them anyway with this special trick. SQL window functions are one of the language’s most powerful features. However, the syntax of window functions is not easy to master. It has lots of details that can cause beginners to stumble. One of the most common traps is trying to use window functions in GROUP BY.

Marija Ilic

7 Common GROUP BY Errors

Are you making these errors with GROUP BY in SQL? Find out what they are, how to avoid them, and how to fix them. SQL’s GROUP BY statement can quickly uncover powerful data insights. At first, using GROUP BY can seem easy – e.g. when creating basic SQL reports that you’ll present to business decision-makers. But while learning this powerful feature, you could become trapped in weird errors or get incorrect results caused by improperly written GROUP BY statements.

Tihomir Babic

An Overview of Aggregate Functions in SQL

Aggregate functions are commonly used in SQL. This article will lead you through their use and show examples of how they work. SQL aggregate functions are a useful tool, especially for creating reports. They’re not difficult to understand, especially if you have some experience with Excel or similar programs. You’ve probably used aggregate functions like SUM or AVERAGE in a spreadsheet. Even if you only occasionally use them, knowing aggregate functions can help you better understand your data and work more efficiently.

Tihomir Babic

How to Use CASE WHEN With SUM() in SQL

This article will teach you what a CASE WHEN expression is in SQL and how to use it with a SUM() function and a GROUP BY statement. The examples are included to bolster your understanding. Knowing how to use a CASE WHEN expression in SQL adds insight into the exciting possibilities in SQL. It elevates you from a simple user who depends on what SQL returns, to a user who is more in command and who sets specific criteria in SQL.

LearnSQL.com Team

SQL Course of the Month – GROUP BY Extensions in SQL

Do you want to develop your SQL skills? Do you want to get more out of your data and prepare better reports and summaries? The answer is learning to use SQL’s GROUP BY extensions. But how should you go about this? I asked the same question to Agnieszka Kozubek-Krycuń, Vertabelo’s Chief Content Officer. As she explains, the secret is in this November’s free SQL Course of the Month: GROUP BY Extensions in SQL.

Tihomir Babic

What is the Difference Between COUNT(*), COUNT(1), COUNT(column name), and COUNT(DISTINCT column name)?

Have you noticed there are different variations of the SQL COUNT() function? This article explains the various arguments and their uses. As a SQL user, you’re probably quite familiar with the COUNT() function. Even though it’s relatively simple, it can be used in several different ways. Each way has a very different use. I imagine you’ve seen code that contains the function COUNT(*) or COUNT(1). You’ve probably also seen some other uses of the COUNT() function, such as COUNT(column name) and COUNT(DISTINCT column name), even if you haven’t used them.

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.

Kateryna Koidan

GROUP BY in SQL Explained

The SQL GROUP BY statement is easy to use, but it can be hard to master. Learn what you can do with GROUP BY, how it works, and how to use it with aggregate functions. GROUP BY is one of the basic SQL tools. However, it might be difficult for beginners to understand how GROUP BY works and how it is used to compute statistics with different aggregate functions. In this article, I’ll use several examples to show exactly how GROUP BY organizes rows and how aggregate functions can be used to calculate statistics on one or more columns.

Zahin Rahman

How to Find Duplicate Values in SQL

Duplicate records waste time, space, and money. Learn how to find and fix duplicate values using SQL’s GROUP BY and HAVING clauses. Database best practices usually dictate having unique constraints (such as the primary key) on a table to prevent the duplication of rows when data is extracted and consolidated. However, you may find yourself working on a dataset with duplicate rows. This could be because of human error, an application bug, or uncleaned data that’s been extracted and merged from external sources, among other things.

Ignacio L. Bisso

How Does SQL GROUP BY Work?

Grouping results is a powerful SQL feature that allows you to compute key statistics for a group of records. GROUP BY is one of SQL’s most powerful clauses. It allows you to see data in a new way and find key metrics (like the average, maximal, and minimal values in a group of records). Without GROUP BY, all the results we obtain are oriented to records. With GROUP BY, we can create groups of records and calculate metrics on each group.

Adrian Więch

5 Examples of GROUP BY

When you start learning SQL, you quickly come across the GROUP BY clause. Data grouping—or data aggregation—is an important concept in the world of databases. In this article, we’ll demonstrate how you can use the GROUP BY clause in practice. We’ve gathered five GROUP BY examples, from easier to more complex ones so you can see data grouping in a real-life scenario. As a bonus, you’ll also learn a bit about aggregate functions and the HAVING clause.

Martyna Sławińska

What Is the Difference Between WHERE and HAVING Clauses in SQL?

As the amount of data in the world grows day by day, the need increases for managing and querying data efficiently. SQL offers ways to manipulate and query data at any scale. As an important part of this, the WHERE and HAVING clauses allow you to filter data as you need, but they are not the same. We will explain the differences between them in detail. One of the most common tasks in manipulating and querying data is filtering using the WHERE and HAVING clauses.

Dorota Wdzięczna

The SQL HAVING Clause Explained

What is the SQL HAVING clause? Why do you need it, and where do you use it? We’ll explain HAVING in detail. HAVING is a very common clause in SQL queries. Like WHERE, it helps filter data; however, HAVING works in a different way. If you are familiar with the GROUP BY clause and have only heard about HAVING – or if you’re not familiar with HAVING at all – this article is what you need.

Zahin Rahman

Using GROUP BY in SQL

Now that you know SQL’s core commands, power up your queries with the GROUP BY clause and aggregate functions. GROUP BY is a SQL clause that arranges data into groups based on a common value (or values). It is widely used to obtain summary information for large datasets as well as for computing basic aggregate statistics. Once you have grasped SQL’s basic commands like SELECT, WHERE, and JOIN, mastering the GROUP BY clause can help you implement your SQL knowledge in real-world business intelligence scenarios.

Emil Drkušić

What Is the Difference Between a GROUP BY and a PARTITION BY?

Window functions are a great addition to SQL, and they can make your life much easier if you know how to use them properly. Today, we will address the differences between a GROUP BY and a PARTITION BY. We’ll start with the very basics and slowly get you to a point where you can keep researching on your own. PARTITION BY vs. GROUP BY The PARTITION BY and the GROUP BY clauses are used frequently in SQL when you need to create a complex report.

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.

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.

Francisco Claria

A Beginner’s Guide to SQL Aggregate Functions

Aggregate functions are powerful SQL tools that compute numerical calculations on data, allowing the query to return summarized information about a given column or result set. These functions can be used in conjunction with the GROUP BY statement. Let’s see how they work using some easy examples. SQL Aggregate Functions Suppose we have users residing in a city, and we store their information in two tables. These tables and their relationship are shown below:

Marian Dziubiak

Getting the Hang of the GROUP BY Clause

GROUP BY is an important part of the SQL SELECT statement. But new SQL coders can run into some problems when this clause is used incorrectly. Here’s how to avoid those issues. You’re learning SQL. You know how to SELECT some data FROM a table and how to filter the data with a WHERE clause. You can process the data using aggregate functions (MIN, MAX, SUM, AVG, and others). But when you’re dealing with a lot of data, you may need to narrow it down even more.

Agnieszka Kozubek-Krycuń

GROUP BY Clause: How Well Do You Know It?

The database can do different kinds of computations: it can add and subtract, multiply and divide, it can do computations on dates, it can count rows and sum row values, and so on. It can also do quite sophisticated statistics. The GROUP BY clause is the most basic way to compute statistics in SQL. It can be quite tough for beginners but it is really powerful. Let's look at the details of the GROUP BY clause, starting with the basics.