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Lesson 10 - MySQL Step By Step: Subqueries

In the previous lesson, MySQL Step By Step: Exercises to practise, we practiced queries on several examples. Today's lesson is all about subqueries, so it's going to complete our knowledge of the SQL basics.

Subqueries

A subquery is a query that's part of another query. Right, we can nest queries into another. Like this, we can use the output of one query as an input for another query because it's basically also a data table. In practice, this is widely used, and we have the ability to get all the results straight from the database that we'd otherwise have to put together in our application.

Of course, subqueries are performance-intensive, but if they're optimized properly (see the next lessons) they should be faster than using multiple separate queries or JOINs.

Try to think about how'd you list articles of the user whose nickname is "David". You might think of the following query:


 

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In this tutorial, we'll learn to use subqueries, nested queries in MySQL database. We'll explain new operators: IN, ALL, ANY, and EXISTS.

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Article has been written for you by David Capka
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The author is a programmer, who likes web technologies and being the lead/chief article writer at ICT.social. He shares his knowledge with the community and is always looking to improve. He believes that anyone can do what they set their mind to.
Unicorn College The author learned IT at the Unicorn College - a prestigious college providing education on IT and economics.
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