24 Oct 2024 Agnieszka Kozubek-Krycuń NULLs and Handling Missing Data in SQL Handling missing data (i.e. NULLs) in SQL can be challenging. NULLs can pose a lot of traps, especially if you don’t understand how they work. In this article, we’ll talk about dealing with NULL in SQL. We’ll also explain how to avoid common mistakes when working with NULLs. Having missing data in your database is an unavoidable reality of life. There are many reasons why you may have missing data in your database: the complete data isn’t yet available, users provide incomplete information, changes to the database schema, database malfunctions, human error, and more. Read more 29 May 2024 Agnieszka Kozubek-Krycuń Top 100+ SQL Interview Questions and Practice Exercises Are you gearing up for a SQL interview? This article is packed with over 100 SQL interview questions and practical exercises, organized by topic, to help you prepare thoroughly and approach your interview with confidence. SQL is essential for many jobs, like data analysis, data science, software engineering, data engineering, testing, and many others. Preparing well for a SQL interview is crucial, no matter what role you're aiming for. Read more 13 May 2024 Agnieszka Kozubek-Krycuń SQL FIRST_VALUE Function Discover the power of the FIRST_VALUE function, a window function that returns the first value in an ordered partition of the result set. This function is useful for anyone doing data analysis in SQL. Window functions are a powerful category of functions that enable doing sophisticated data analysis in SQL. These functions operate over a "window" of rows related to the current row, allowing for preparing complex reports like running totals, moving averages, preparing rankings, and others. Read more 23 Apr 2024 Agnieszka Kozubek-Krycuń SQL LEAD Function Get to know the SQL LEAD function, an important function to know for anyone working with SQL in data analysis. Learn through examples how to use this function in practice. The SQL LEAD function is a very important and useful SQL window function. SQL window functions are essential for doing efficient data analysis. They allow you to work with groups of rows and single rows at the same time. They make writing complex reports easier. Read more 16 Apr 2024 Agnieszka Kozubek-Krycuń SQL MAX Function Learn about the SQL MAX function, which is used to find the highest value in your dataset. This article explains how to use the syntax of MAX function and shows typical usage examples. The SQL MAX function is an aggregate function that returns the maximum value in a column. MAX function, together with its counterpart MIN function, is useful for summarizing data in data analysis. It can help you to compute the range of values in a dataset. Read more 27 Jan 2021 Agnieszka Kozubek-Krycuń Why Aren’t SQL Window Functions Allowed in GROUP BY? It’s true – the SQL order of operations means window functions aren’t allowed in GROUP BY. But you can use them anyway with this special trick. SQL window functions are one of the language’s most powerful features. However, the syntax of window functions is not easy to master. It has lots of details that can cause beginners to stumble. One of the most common traps is trying to use window functions in GROUP BY. Read more 14 Jan 2021 Agnieszka Kozubek-Krycuń 2021 Monthly SQL Practice and New 2020 Practice Course Did you know that LearnSQL.com provides a monthly SQL Challenge? Every month, we publish a new set of SQL practice exercises. Find out what to expect from our SQL challenges in 2021. Here at LearnSQL.com, we believe that the best way to learn SQL is through practice. After all, writing SQL is a practical skill. That’s why all our SQL courses (and there are over 30 of them!) are interactive: You learn SQL by writing SQL code. Read more 8 Dec 2020 Agnieszka Kozubek-Krycuń The History of SQL Standards Has the SQL standard changed in the 30+ years it's been around? Absolutely! Learn about the journey from SQL-86 to modern SQL, today’s standard data language. SQL was created in the early 1970s by IBM. In 1974, Donald Chamberlin and Raymond Boyce published the article SEQUEL: A Structured English Query Language, which introduced SQL to the world. The article contained the BNF grammar (a detailed technical description of the language syntax) for the language, which IBM later thought was a mistake. Read more 2 Dec 2020 Agnieszka Kozubek-Krycuń SQL Technologies Are More Common Than You Think Where is SQL being used today? The answers might surprise you! (Hint: SQL technology is basically everywhere.) Is it worth learning SQL? After all, the language was created in the 1970s. Is it still relevant today? The list of technologies that support SQL is very long – and it’s growing. Read on to find out what kinds of programs use SQL. SQL in Databases Relational Databases = SQL Databases It’s no surprise that SQL is used in relational databases. Read more 17 Nov 2020 Agnieszka Kozubek-Krycuń The History of SQL – How It All Began Who created SQL and why? Find out in this article! Here’s a brief history of SQL, starting with its foundational concept: the database. Ted Codd and the Relational Data Model The first computer databases appeared in the late 1960s. This was an important area of research at the time. Many computer scientists were focused on improving how databases work. One of them was Edgar Frank (Ted) Codd, an English computer scientist employed at IBM. Read more «« « 1 2 3 » »»