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Converting Subqueries to Joins

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Not all queries are alike, especially in terms of performance. In this article, we’ll look at how you can convert SQL subqueries to joins for improved efficiency. When should I use SQL subqueries? Great question! Unfortunately, there’s no concrete answer. SQL beginners tend to overuse subqueries. Typically, once they find that SQL construction works in one situation, they try to apply that same approach to other situations. It’s only natural. However, in some cases a subquery can be replaced with

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How It Works

Brush up on your data science and SQL skills with Vertabelo Academy’s interactive courses. Why Vertabelo Academy? You get instant access to lessons that teach various concepts of SQL, data science, and programming in R (soon also in Python!). Our courses are appropriate for people who have no prior knowledge of computer science or programming. The only requirement is a web browser. No need to install databases, download example tables, or spend time inventing exercises for yourself. Each course comes with

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Understanding Data: Mining Vs. Visualization

Here’s a reality check: Big Data has hit us like a speeding truck on the highway of business intelligence. In today’s digital age, we’re generating data about ourselves that were once considered private, and we’re doing it willingly! From what we eat and wear to where we are at all times, nearly everything is now public knowledge. The data generated is a potential diamond mine for everyone in business, from one-person companies to Fortune 500 A-Listers alike, all thanks to

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Must-Know SQL Terms for Beginners and Pros

Working with databases can seem daunting to a non-technical person. Right away, you’re bombarded with new terms that make your head spin. Database, database instance, table, SQL and others are some of the basic terms that you need to understand just to have a normal conversation with your technical colleagues. In this article, we’ll explore some basic database terminology you need to know to succeed. Imagine you’re attending a meeting with the development staff and suddenly feel as if you’re

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SQL Interview: Tips From Recruiter and Sample Questions with Solutions

Applying for an SQL-related position? You’ll likely have to pass an interview process. But you’ll be much better prepared for the interview if you know what to expect. This article sheds some light on the recruiter’s perspective to better prepare you for your interview.   SQL Knowledge and Skills There are different SQL skills that an interview can test. These include: Skills related to any specific SQL database engine (like PostgreSQL, MySQL, or Oracle). Skills associated with SQL clients or

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Correlated Subqueries in 5 Minutes

If you’re familiar with the famous Russian nesting doll, then SQL subqueries should be a peace of cake to understand—subqueries are just queries nested within queries. An SQL subquery is often called an “inner” query; the main query is usually called the “outer” query. This article covers everything you need to know about correlated subqueries. What Exactly is a Correlated Subquery? A correlated SQL subquery is just a subquery that is executed many times—once for each record (row) returned by

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