Articles Cookbook
12 Oct 2017
Ignacio L. Bisso

SQL Window Functions By Explanation

In our previous post, we explained how SQL window functions work by example. We started with some very simple, basic functions. Let's extend it by explaining subclauses in window functions. SQL window functions are a great way to compute results from a set of rows rather than a single row. As you know from our first article, the "window" in window function refers to the set of rows. We showed you some examples of simple window functions like RANK and LEAD.
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10 Oct 2017
Aldo Zelen

Long SQL Query vs. Recursive SQL Query

Recursion is one of the central ideas in computer science. We can define it as a method for solving problems where the solution of the problem depends on solving a smaller instance of a problem. If this sounds complicated do not fret, in this article we will learn about recursion in SQL that you can practice and deepen at LearnSQL.com. Recursion is a way of solving hierarchical problems we find in data with common SQL.
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28 Sep 2017
Dorota Wdzięczna

An Illustrated Guide to Multiple Join

So far, our articles in the "An Illustrated Guide" series have explained several join types: INNER JOINs, OUTER JOINs (LEFT JOIN, RIGHT JOIN, FULL JOIN), CROSS JOIN, self-join and non-equi join. In this final article of the series, we show you how to create SQL queries that match data from multiple tables using one or more join types. Join Types in SQL Queries Before we start discussing example SQL queries that use multiple join types, let's do a short recap of the join types we've covered so far, just to be sure you understand the differences.
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24 Sep 2017
Dorota Wdzięczna

An Illustrated Guide to the SQL Non Equi Join

Did you know that in SQL, a join doesn’t have to be based on identical matches? In this post, we look at the SQL non equi join, which uses ‘non-equal’ operators to match records. We’ve already discussed several types of joins, including self joins and CROSS JOIN, INNER JOIN and OUTER JOIN. These types of joins typically appear with the equals sign (=). However, some joins use conditions other than the equals (=) sign.
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21 Sep 2017
Dorota Wdzięczna

An Illustrated Guide to the SQL Self Join

What is an SQL self join and how does it work? When should it be used? We’ll provide answers to those questions! In SQL, we can combine data from multiple tables by using a JOIN operator. JOIN has several variants; we’ve already discussed CROSS JOIN, INNER JOIN, and OUTER JOIN. Most of the time, these operators join data from two or more different tables. You can practice all the different types of JOINs in our interactive SQL JOINs course.
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4 Sep 2017
Marija Ilic

How to Track Down Duplicate Values in a Table

When it comes to information management, duplicates present one of the most common challenges to data quality. In this article, I'll explain how it is possible to find and distinguish duplicate names with the help of the SQL data programming language. I really like my maiden name. The reason I like it so much is because it's rare. My maiden name (first with last) provided a unique identifier on platforms such as LinkedIn, Facebook, Twitter and similar.
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31 Aug 2017
Aldo Zelen

Common SQL Window Functions: Positional Functions

Positional SQL window functions deal with data's location in the set. In this post, we explain LEAD, LAG, and other positional functions. SQL window functions allow us to aggregate data while still using individual row values. We've already dealt with ranking functions and the use of partitions. In this post, we'll examine positional window functions, which are extremely helpful in reporting and summarizing data. Specifically, we'll look at LAG, LEAD, FIRST_VALUE and LAST_VALUE.
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28 Aug 2017
Jenny Hung

Four Reasons You Must Learn SQL in Data Science

Is SQL important for data science? It certainly is! This language can help you build a foundation for your analytical career. Let’s see how you use SQL in data science. Data science is hot right now. What if you could predict the next market crash? Or contain the spread of Ebola? Or accurately predict a health crisis months or even years before it happens? Data scientists are working hard on these kinds of projects, and they are earning healthy salaries in the process.
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21 Aug 2017
Kamila Ostrowska

5 Reasons Why No One Should Be Afraid to Learn SQL

Think SQL is just for tech experts? Think again. In this article, we'll bust some common myths and show you that anyone can learn SQL. Let's dive in and make SQL simple. In today’s world, even those in non-technical jobs need some technical skills. And you don’t have to be a hard-core nerd to get these skills. Everywhere you look, from marketing to management, a touch of tech knowledge can set you apart.
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17 Aug 2017
Francisco Claria

Referential Constraints and Foreign Keys in MySQL

Foreign keys and referential constraints allow you to set relationships between tables and modify some of the database engine’s actions. This beginner’s guide explains referential integrity and foreign key use in MySQL. One of the most important aspects of database usage is being able to trust the information you store. Database engines provide several features that help you maintain the quality of your data, like defining required columns as NOT NULL and setting an exact data type for each column.
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