Introduction to Modern Databases/

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Using EXPLAIN Plans

Using EXPLAIN Plans

Learn how to use and analyze SQL execution plans with the EXPLAIN command to optimize query performance.

We'll cover the following...

Imagine our OnlineStore is preparing for a massive holiday sale.

Imagine this: the product search page suddenly starts taking forever to load. Customers get frustrated and leave the site. You suspect the database query that fetches products is to blame—but how can you be sure? More importantly, how do you fix it? You can’t just rewrite the query and hope for the best. You need a way to look under the hood and see exactly how the database is executing your query.

That’s where an execution plan comes in. Learning to read and interpret execution plans is like gaining a superpower for database performance tuning.

By the end of this lesson, we will be able to:

  • Understand what a query execution plan is and why it’s essential for performance tuning.

  • Learn how to generate an execution plan using the EXPLAIN command.

  • Identify key components of an EXPLAIN plan, such as scan types and join algorithms.

  • Analyze a simple execution plan to spot potential performance issues.

Let’s dive in and learn how to become database detectives!

Query execution plan

Whenever we send a SQL query to the database, it doesn’t just run it blindly.

Instead, a very smart component called the query optimizer kicks in. Its job is to determine the most efficient way to obtain the data we requested. It considers various strategies, such as which table to access ...