19 Mar 2021 Marija Ilic 7 Real-Life Situations When You Need a Running Total and How to Compute It in SQL Do you want to learn what a running total is and how to compute it SQL? In this article, I will describe different business scenarios in which a running total is needed. I will also teach you how to calculate a running total in SQL with the help of window functions. Ready? Let’s go! Running Total Definition A running total is the cumulative sum of a value and all previous values in the column. Read more 16 Feb 2021 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. Read more 26 Jan 2021 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. Read more 18 Dec 2020 Marija Ilic How SQL Window Functions Can Help Managers Decide Who Gets a Raise Window functions are one of the most powerful features in modern SQL. In this article, you will learn why window functions are so great. I will list you the most useful window functions and briefly explain when and how you can use them. Simple SELECT statements, in combination with WHERE, GROUP BY, and HAVING, are sufficient for many analyses at work. I used standard SQL for many years before I realized there is something more. Read more 12 Nov 2020 Marija Ilic SQL JOIN Types Explained What’s the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN in SQL? When should you use each one? We’ve got your answers right here. You want to combine data from two or more different tables, but you’re not sure how to do it in SQL. No worries. In this article, I will show you how to use the SQL JOIN clause to merge data from two tables. Read more 9 Oct 2020 Marija Ilic How to Join the Same Table Twice JOIN is one of the most common statements in SQL. As you may know, it is used to join and combine data from two or more tables into one common data set. In this article, I’m going to discuss special types of joins? in which you combine the same table twice—including joining a table to itself, also known as the self join. When and why do you need to do this? Read more 7 Oct 2020 Marija Ilic How to Create Your First Table in SQL Creating a database table with SQL is one of the core skills you’ll need to work with data. And it’s easy to learn, so let’s get started! Imagine you’re analyzing data and want to store your results in a database table. Sure, you've done this a million times in Excel. But you’re not sure how to create a table with SQL. Or maybe you’ve noticed that data engineering is in high demand and you want to start learning its core concepts. Read more 4 Sep 2020 Marija Ilic What a Moving Average Is and How to Compute it in SQL Want to dive deep into time series data and examine long-term trends? Want to know what a moving average is and how to compute it in SQL? Then this article is for you. I’ll explain a powerful feature in SQL called window functions and show how you can calculate moving averages using them. The best way to learn about SQL window functions is the interactive Window Functions course at LearnSQL. Read more 23 Jul 2020 Marija Ilic How to Analyze a Time Series in SQL Values ordered by time are called a time series. In this article, I’ll show you the most frequent patterns and teach you how to write queries for time series in SQL with the help of window functions. Maybe you’ve had the opportunity to analyze some variables where each value was associated with a time value. Such data – where values are ordered by time – is called time series data. Read more 9 Jul 2020 Marija Ilic What Is a CTE? After mastering statements like SELECT, DELETE, INSERT, and GROUP BY, you might search for ways to improve code maintainability, reproducibility, and readability. At that point, you will probably start learning about modern SQL concepts that were introduced in the early 2000s. One such SQL technique is the CTE? (common table expression) —?a temporary named result set. In this article, you will learn what a CTE is and how to use it to improve the maintenance and the readability of your code. Read more «« « 1 2 » »»