28 Feb 2023 Ignacio L. Bisso 25 Advanced SQL Query Examples One of the best ways to learn advanced SQL is by studying example queries. In this article, we'll show 25 examples of advanced SQL queries from medium to high complexity. You can use them to refresh your knowledge of advanced SQL or to review before a SQL interview. Many of the examples in this article will be based on the following employee table. Only a few examples will be based on other tables; in these cases, the tables will be explained along with the example. Read more 29 Dec 2022 Ignacio L. Bisso How to Practice SQL Subqueries Have you ever wondered what separates beginners from advanced SQL users? It includes things like, for example, subqueries. In this article, I explain their importance and why you need to practice SQL subqueries to become an expert. What Is an SQL Subquery? SQL is an easy-to-learn language. However, there are certain complex features and techniques of the language that require practice. One of these features is the subquery, which adds great expressive power to the language and your projects. Read more 29 Nov 2022 Ignacio L. Bisso What Data Type to Choose for a Column When Creating a Table in SQL Databases store data values of various kinds. For example, you may store the name of a product as a text string, the price of a product as a number, or the date a product is sold as a date value. These values – the product name, the price, and the sale date – are stored as different data types. In this article, we explain several SQL data types with real examples. Read more 27 Oct 2022 Ignacio L. Bisso What Are the Basic SQL Queries? You can access the data in a database using some basic SQL queries. In this article, we review the fundamentals SQL queries every beginner should know. Databases are everywhere, and they contain different kinds of data. Almost all of them support SQL, a language that lets you read and manipulate the data inside a database. In this article, I’ll show you the basic SQL queries that you can use to perform many common everyday data tasks. Read more 29 Sep 2022 Ignacio L. Bisso How the WITH Clause Works in SQL Do you want to master complex SQL queries? Learn how to use the powerful WITH clause! In SQL, there are simple queries and complex queries. A simple query can take data from a table, apply a filter, and return the data as it is in the source table. A complex query may require complex transformations to the source data or may need to read and join data from multiple tables or views. Read more 30 Jun 2022 Ignacio L. Bisso Learn the OVER() Clause in SQL with 7 Examples Learn how to use the OVER() clause in your SQL queries and you will take a step forward in your SQL knowledge. Most data analysts and SQL developers have a good handle on the SELECT, FROM, WHERE, GROUP BY, and ORDER BY clauses. However, these clauses are only a limited subset of the SQL language. There are other clauses, such as OVER(), which allow us to create flexible SQL reports and add an enormous expressive power to the SQL language. Read more 24 May 2022 Ignacio L. Bisso How to Use the COALESCE() Function in SQL SQL users are often faced with NULL values in their queries and need to process them properly. The COALESCE() function helps handle NULL values. Read this article to learn how to use COALESCE() in your queries. SQL tables store data in records, and records are composed of fields. There can be situations where we don’t know the value for a specific field. For example, let’s suppose we have a table with data for persons. Read more 31 Mar 2022 Ignacio L. Bisso How to Use the ROUND() Function in SQL Need to round numeric results in SQL? The ROUND() function is here to do the job. Modern relational databases offer many built-in functions that extend the capabilities of SQL. In this article, we will use practical examples to explain how the ROUND() function works. (Spoiler alert: If you guessed that it rounds a number to a certain decimal place, you’re right! Read on to find out more.) SQL Standard Functions Each SQL database (PostgreSQL, MySQL, Oracle, SQL Server among others) has a set of built-in functions. Read more 19 Jan 2022 Ignacio L. Bisso What Is a Common Table Expression (CTE) in SQL? The common table expression (CTE) is a powerful construct in SQL that helps simplify a query. CTEs work as virtual tables (with records and columns), created during the execution of a query, used by the query, and eliminated after query execution. CTEs often act as a bridge to transform the data in source tables to the format expected by the query. A common table expression, or CTE, is a temporary named result set created from a simple SELECT statement that can be used in a subsequent SELECT statement. Read more 23 Dec 2021 Ignacio L. Bisso How to Use the SQL PARTITION BY With OVER At the heart of every window function call is an OVER clause that defines how the windows of the records are built. Within the OVER clause, there may be an optional PARTITION BY subclause that defines the criteria for identifying which records to include in each window. Read on and take an important step in growing your SQL skills! What Is the PARTITION BY Clause in SQL? The SQL PARTITION BY expression is a subclause of the OVER clause, which is used in almost all invocations of window functions like AVG(), MAX(), and RANK(). Read more «« « 1 2 3 … 5 » »»