Spooky Scary NULL: Unexpected Danger Lurking in Your Database

NULL, NOT NULL,

Relational databases often store the value NULL in their tables. If you’re not familiar with NULL and what it is, you could run into unexpected problems. In this article, we’ll take a look at how the IN and EXISTS operators work with NULL. What Is NULL? In SQL, NULL is a special value indicating that a particular piece of data doesn’t exist in the database. For SQL beginners, it’s often a source of problems. Each column in a table requires

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Popular SQL Interview Questions for Business Analysts

SQL is an extremely desirable skill for anyone in today’s market—not just those in the IT sector. It’s becoming increasingly common for employers to require at least a basic knowledge of SQL in professions related to finance, statistics, banking, and business analytics. In this article, we will focus on the SQL questions one can expect during an interview for a business analyst (BA) position. What is a Business Analyst? Simply put, a BA is someone who analyzes a variety of

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Why Learn SQL?

Nowadays, data are gathered from a variety of sources, and information is of great value to organizations. However, with an increasing amount of data comes the need for databases that can store information for retrieval and analysis by trained specialists. Thus, proper data analysis is in high demand in our digital world. Relational databases, which logically group information into chunks, are basically used to store and organize large amounts of data. Of course, if you’re looking to retrieve any kind

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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

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An Illustrated Guide to the SQL Non-Equi Join

Did you know that an SQL join doesn’t have to be based on identical matches? In this post, we look at the 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. These are called non-equi joins, and they’re what we will

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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. In this article, however, we will explain how to join records from the same table. A self-join

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