How to Calculate the Difference Between Two Rows in SQL by Ignacio L. Bisso 14 Jul 2020 Calculating the difference between two rows in SQL can be a challenging task. It is possible – and there’s more than one way to do it. In this article, I’ll explain how to use the SQL window functions LEAD() and LAG() to find the difference between two rows in the same table. I like to think of this as a “happy hour" article – you can learn about two topics (calculating the difference between two rows and SQL window functions) by reading just one article. Read more How to Number Rows in an SQL Result Set by Ignacio L. Bisso 21 May 2020 Have you ever needed to add a sequential number to the records in the result of an SQL query? It’s not as simple as it looks! Find out how to do it correctly in this article. To number rows in a result set, you have to use an SQL window function called ROW_NUMBER(). This function assigns a sequential integer number to each result row. However, it can also be used to number records in different ways, such as by subsets. Read more Beginner’s Guide to the SQL Subquery by Ignacio L. Bisso 14 May 2020 Subqueries are a powerful SQL resource, allowing us to combine data from multiple tables in a single query. In this article, we’ll teach you everything you need to begin using subqueries. Perhaps the simplest definition of a SQL subquery is “A query inside a query”. Subqueries are so easy to understand that they often appear in the opening chapters of SQL courses. However, there are many variants of subqueries that need to be explained. Read more SQL Window Functions vs. GROUP BY: What’s the Difference? by Ignacio L. Bisso 8 Apr 2020 A very common misconception among SQL users is that there is not much difference between SQL window functions and aggregate functions or the GROUP BY clause. However, the differences are very significant. Perhaps the only similar point between GROUP BY and window functions is that both allow you to execute a function (such as AVG, MAX, MIN, or COUNT) on a group of records. I’d say that window functions’ special power is that they allow us to obtain results that otherwise would be almost impossible to achieve. Read more HAVING vs. WHERE in SQL: What You Should Know by Ignacio L. Bisso 6 Feb 2020 This article is about SQL’s WHERE and HAVING clauses. Both clauses are part of the foundations of the SQL SELECT command. They have similar uses, but there are also important differences that every person who uses SQL should know. Let’s see what’s behind the HAVING vs. WHERE debate. In this article, we’ll suppose we work for a government social agency supporting people or families whose income is below a certain threshold. Read more SQL Order of Operations by Ignacio L. Bisso 8 Oct 2019 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. Read more SQL INNER JOIN Explained in Simple Words by Ignacio L. Bisso 30 Apr 2019 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? Read more A Non-Technical Introduction to Learning SQL on Your Lunch Break by Ignacio L. Bisso 7 Feb 2019 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. Read more How to Install PostgreSQL on Windows 10 in 5 Minutes by Ignacio L. Bisso 15 Nov 2018 It may look like a complicated task to install PostgreSQL, Oracle, or SQL Server or any other database software, but it really isn’t! These days, most relational database management systems come with installation wizards that make the process much simpler. In this article, we’ll look at how to install PostgreSQL and test that the installation is working. Install PostgreSQL: Steps Involved To install PostgreSQL, we’ll complete the following tasks: Read more How to Begin Running SQL Queries by Ignacio L. Bisso 27 Sep 2018 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. Read more «« « 1 2 3 » »»