30 Sep 2021 Ignacio L. Bisso What Is the OVER() Clause in SQL? Window functions are one of SQL’s most powerful resources, but they are not frequently used by the average SQL developer. In this article, we will explain how you can define different kinds of window frames using the OVER clause. The OVER clause is essential to SQL window functions. Like aggregation functions, window functions perform calculations based on a set of records – e.g. finding the average salary across a group of employees. Read more 5 Aug 2021 Ignacio L. Bisso How to Define a Window Frame in SQL Window Functions The window function is a super powerful resource of the SQL language. At the core of any window function, there is a set of records, called the window frame, defined using an OVER clause. Knowing what records are in the window frame, how they are ordered, and what their upper and lower bounds are, are critical in understanding how window functions work. In this article, we will analyze and explain with examples how you can define different types of window frames. Read more 16 Jul 2021 Ignacio L. Bisso Top 10 SQL Window Functions Interview Questions Many interesting job positions require SQL skills – and that includes window functions, which are not commonly taught in online courses. In this article, I will cover the top window function questions for every experience level. If you’re going for a job interview for an advanced SQL position or for intermediate to advanced data analyst positions, you’ll probably be asked about your knowledge of SQL window functions. Don’t panic! Although these functions aren’t commonly covered in online courses, we’ve got the answers right here. Read more 26 May 2021 Ignacio L. Bisso How to Compute Year-Over-Year Differences in SQL How did your business do this year compared to last year? The year before? Find out how to use SQL to calculate year to year and month to month differences. Year-over-year (YOY) comparisons are a popular and effective way to evaluate the performance of several kinds of organizations. Year to year differences are easy to understand – e.g. it’s easy to understand that your revenue growth is 35% year to year. Read more 29 Apr 2021 Ignacio L. Bisso Why Do You Need a Primary Key in a Database Table? What is a primary key and why is it so important in SQL? Find out in this article. Primary keys are a central element in SQL databases. They provide a unique value that can identify a specific row in a table, which opens up a lot of other benefits. This article covers what a primary key is, how it works, and how to use it in an SQL database. Read more 24 Mar 2021 Ignacio L. Bisso What Is a NOT NULL Constraint in SQL? SQL has several ways of dealing with NULLs. In this article, we’ll focus on the NOT NULL constraint and other NULL-related clauses. Understand this and you’ll take an important step in your SQL growth! Before we get straight into the NOT NULL constraint, let’s quickly define what NULLs and constraints are. NULL values are a central concept in SQL databases. The idea behind a NULL value is simple: a NULL value means that we do not have a known value for that field. Read more 29 Jan 2021 Ignacio L. Bisso Data Types in SQL Read this article and learn the ABC of SQL data types. Data types are used to define the type of data stored in a database. However, there are related concepts that a good SQL developer should know: data type conversion, what operations are possible between different data types, date arithmetic, etc. SQL also provides functions that manipulate values of different data types (i.e. functions for string data, date and time data, etc. Read more 25 Dec 2020 Ignacio L. Bisso What Is a Database Index? Database indexes are critical to query speed and efficiency. Learn when, why, and how to use them – and when not to – in this post. Indexes are very important database objects; they optimize data access and improve database performance by helping the database execute SQL queries faster. Why not take this opportunity to learn how indexes work and how to create them? What Is a Database Index? Indexes are data structures that can increase a database’s efficiency in accessing tables. Read more 27 Nov 2020 Ignacio L. Bisso What Is a Foreign Key in SQL? What does a foreign key do in SQL? Why would you need one? Learn the ABCs of foreign keys in five minutes. Foreign keys are a central concept in SQL databases; they allow us to enforce data consistency. Usually they work with primary keys to connect two database tables, like a virtual bridge. All SQL developers need to know what SQL foreign keys are, how they work, what data values are allowed in them, and how they’re created. Read more 22 Oct 2020 Ignacio L. Bisso What is a Primary Key in SQL? Primary keys are an important concept in SQL databases. They provide a unique ID for every row in a database table. As an SQL developer, you should know what primary keys are, what data values are allowed in them, and how to create them. Read this article to learn the ABCs of primary keys in 10 minutes. How to Identify Rows in a Table Tables are the main objects in an SQL database, and as you probably know, tables store records or rows. Read more «« « 1 2 3 4 » »»