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 24 Sep 2020 Ignacio L. Bisso What Is the MySQL OVER Clause? If you want to learn window functions in MySQL, you need to understand the OVER clause. In this article, we use real-world examples to explain what the MySQL OVER clause is, how it works, and why it’s so awesome. In 2018, MySQL introduced a new feature: window functions, which are accessed via the OVER clause. Window functions are a super powerful resource available in almost all SQL databases. They perform a specific calculation (e. Read more 27 Aug 2020 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. Read more 30 Jul 2020 Ignacio L. Bisso How to Use Subqueries in INSERT, UPDATE, and DELETE Statements Did you know that subqueries can also be used in UPDATE, INSERT, and DELETE statements? Subqueries in SQL are like building blocks that can be used in a variety of statements, not just SELECT. If you find subqueries useful in SELECT, read this article to find out how useful they can be in other instructions. You will be able to create much more complex and powerful SQL queries in no time! Read more 14 Jul 2020 Ignacio L. Bisso How to Calculate the Difference Between Two Rows in SQL 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. The best way to learn window functions is our interactive Window Functions course. It contains over 200 hands-on exercise that will teach you all window functions concepts, from simple OVER() clause to complex topics such as combining window functions and GROUP BY clause. Read more 21 May 2020 Ignacio L. Bisso How to Number Rows in an SQL Result Set 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 14 May 2020 Ignacio L. Bisso Beginner’s Guide to the SQL Subquery 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 «« « 1 2 3 4 5 » »»