Articles Cookbook
18 Nov 2021
Kateryna Koidan

5 SQL Subquery Examples

SQL subqueries are basic tools if you want to communicate effectively with relational databases. In this article, I provide five subquery examples demonstrating how to use scalar, multirow, and correlated subqueries in the WHERE, FROM/JOIN, and SELECT clauses. A subquery, or nested query, is a query placed within another SQL query. When requesting information from a database, you may find it necessary to include a subquery into the SELECT, FROM , JOIN, or WHERE clause.
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16 Nov 2021
Kamila Ostrowska

SQL for Startups – Do You Need It?

If you’ve been wondering whether to use SQL in your startup, it’s probably high time to do so. SQL can be an amazing tool for small, fast-growing businesses. But don’t worry if you’re unfamiliar with SQL for startups. Maybe you are not sure what SQL is all about. Don’t worry; you don’t have to make any decisions this second! First, answer these questions: Can you think of any data related to your business – prices, clients, details about clients, production details, budget, costs, strategy, or anything else?
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11 Nov 2021
Martyna Sławińska

What Are Aggregate Functions in SQL, and How Do I Use Them?

Data is your source of knowledge. And thanks to SQL aggregate functions, you can extract the precise knowledge you need from your data efficiently. Read along to find out more. The core SQL aggregate functions are the following: COUNT(column_name | *) returns the number of rows in a table. SUM(column_name) returns the sum of the values of a numeric column. AVG(column_name) returns the average value of a numeric column.
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10 Nov 2021
Jakub Romanowski

A Chat with Anthony DeBarros, Author of Practical SQL

Some make model ships, others collect stamps. I read SQL books. I've read a lot of them, but only a very few deserve to be called really good. Some of them were included in my Best SQL Books list. The good news is that one of them just got a new release. It was great, even better than the previous edition! Moreover, I was able to talk to its author, Anthony DeBarros.
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9 Nov 2021
Himanshu Kathuria

How to Write a WHERE Clause in SQL

We explain how to use the SQL WHERE clause with practical examples. If you have just started learning SQL and want to know how to retrieve or work with only a specific portion of the data stored in your tables, then this article is for you! What is WHERE Clause in SQL? The SQL WHERE clause filters records based on specific conditions; it allows you to selectively retrieve, modify, or delete data in a database.
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5 Nov 2021
Karolina Niewiarowska

How Can SQL Developers Remember Everything They Learn?

Are you at the beginning of your SQL journey? Congratulations, great choice! But you may find the knowledge you gain leaks with time. Find out what SQL developers do to remember everything they learn for a long time. If you learn SQL, the road to the expert level is long, winding, and bumpy. But don't worry – we've all been through it. You know perfectly well it's worth it.
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3 Nov 2021
Andrew Bone

What Is the DELETE Statement in SQL?

This article will explain the use of the DELETE statement, one of the primary methods of removing existing records from your database. First we will run through the syntax, followed by some easy-to-understand examples. The DELETE statement in SQL is extremely useful. It allows you to remove any obsolete or “bad” data from your database tables. You should exercise caution when using the DELETE statement, as the operation is not reversible.
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29 Oct 2021
Ignacio L. Bisso

What Is a Rolling Average and How Do You Compute It in SQL?

In this article, we will show three different examples of using SQL to calculate rolling averages. Learn this and you will take an important step in your SQL growth! A rolling average is a metric that allows us to find trends that would otherwise be hard to detect. It is usually based on time series data. In SQL, we calculate rolling averages using window functions. First, let’s talk about what rolling averages are and why they’re useful.
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28 Oct 2021
Jakub Romanowski

Top 5 Linux Distributions for SQL

The world is divided into Linux lovers and people who have never tried it before. Still working on Windows or macOS? Do you want to learn SQL? Do you know a large proportion of IT professionals use Linux? It's not a coincidence. But which Linux distribution should you choose for learning SQL? Here's my factsheet to help answer that question.   Linux Distribution: What Is It? What is a Linux distribution?
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27 Oct 2021
Kateryna Koidan

SQL Date and Time Functions in 5 Popular SQL Dialects

Are you confused by all the date and time functions used across different SQL dialects? In this article, I summarize the date and time data types used in PostgreSQL, Oracle, SQLite, MySQL, and T-SQL. I also provide examples with the key SQL date and time functions used across these dialects. It’s time to become date and time gurus! Do you want to calculate how often employees are running late for work?
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