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Articles
Cookbook
25 Jan 2022
Tihomir Babic
The SQL OVER() Clause Explained
Here is a detailed explanation of the OVER() clause in SQL window functions. This is a detailed guide on using the OVER() clause in SQL window functions. I will focus specifically on this clause, which requires that you have at least a general idea of how window functions work. To make the best out of this article, take a look at the SQL Window Functions Cheat Sheet. Feel free to have it by your side as we go.
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20 Jan 2022
Andrew Bone
PostgreSQL Interview Questions and Answers
Job interviews are always stressful. Interviewing and getting asked technical questions about PostgreSQL is even more of a challenge! In this article, we’ll cover some of the PostgreSQL interview questions you can expect when applying for a new job. By the end of the article, you should be able to handle most of the questions you are likely to face. We’ve previously covered common questions you can expect at a SQL job interview, but this article will be focused on Postgres specifically.
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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.
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18 Jan 2022
Kamila Ostrowska
The Top 5 SQL Courses and Learning Platforms for 2022
It’s the New Year! Time to start thinking what good you can do yourself in 2022. If you haven’t decided yet, we want to recommend learning something new – specifically, learning SQL. Maybe learning SQL is already on your 2022 to-do list. If so, take it seriously – learning SQL can change your career path and even your life! It makes sense to find the best SQL courses so you can learn effectively.
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13 Jan 2022
Karolina Niewiarowska
Top 10 Beginner Online SQL Courses in 2022
Ready for New Year’s changes? Good, because now you have a perfect chance to achieve something new: Improve your skills by learning SQL! In this article, we’ll point you toward some great online SQL courses to help you meet this goal. SQL, or Structured Query Language, is the language used to communicate with relational databases. When you know SQL, you can add, delete, change, and make calculations using the data in a database.
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11 Jan 2022
Himanshu Kathuria
The Most Popular Databases for 2022
With the number of database products increasing with each passing year, it is important to understand which database best fits your use case. This article lists the top-ranking databases available in the market today. When something that first became popular in the early 1980s is not slowly fading away but is still evolving and becoming more relevant, you know it had to be an important invention. The database is no exception.
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1 Jan 2022
LearnSQL.com Team
New Monthly SQL Practice for January 2022!
Ready for our new SQL challenge? This time, we have prepared some slightly more difficult SQL tasks. Here’s January’s SQL Practice course! This time you will be helping Monica, the owner of an online store. She’d like to analyze her business data and earn more. It’s the perfect opportunity to use your SQL window functions skills. Can you find out how many customers she has in each country? Can you create reports to help her see sales trends?
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30 Dec 2021
Tihomir Babic
How to Include Zero in a COUNT() Aggregate
Explaining how to include zero (0) counts in your SQL query result. Here’s the problem: you want to count something that doesn’t exist, and you want to show your result as zero. How do you do that in SQL? Using the COUNT() aggregate function is a reasonable first step. It will count all the data it finds and return the number of occurrences. But what if there are no occurrences of certain data?
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28 Dec 2021
Karolina Niewiarowska
Here’s How I Started Creating SQL Reports
Once upon a time, there was a girl who was just starting her adventure with learning SQL. As a marketer, one of her tasks was writing reports. Previously, she used Excel, a calculator, and written notes to prepare the reports her boss required. One day, it turned out that she could do her job much faster and easier. That was the day she read about SQL reports for the first time.
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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().
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