Query optimization techniques in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main goal of query optimization in databases?

The main goal is to make queries run faster and use fewer resources by finding the best way to access and process data.

beginner

How does using indexes help in query optimization?

Indexes allow the database to find rows faster without scanning the whole table, similar to using a book's index to find a topic quickly.

intermediate

What is the purpose of the EXPLAIN statement in MySQL?

EXPLAIN shows how MySQL plans to run a query, helping you understand if indexes are used and where the query might be slow.

beginner

Why should you avoid SELECT * in queries for optimization?

Selecting only needed columns reduces data transfer and processing time, making queries faster and less resource-heavy.

intermediate

What is query caching and how does it improve performance?

Query caching stores the result of a query so if the same query runs again, the database can return the stored result quickly without re-running it.

Which of the following helps MySQL find data faster?

A Using SELECT *

B Running queries without WHERE

C Using indexes

D Using ORDER BY on large tables

Indexes speed up data lookup by avoiding full table scans.

What does the EXPLAIN command show in MySQL?

A The query execution plan

B The number of rows in a table

C The database size

D The list of indexes

EXPLAIN shows how MySQL will execute a query, helping identify optimization opportunities.

Why is it better to avoid SELECT * in queries?

A It causes data loss

B It returns all columns, which can slow down the query

C It disables indexing

D It makes the query syntax incorrect

Selecting only needed columns reduces data processing and speeds up queries.

What is a benefit of query caching?

A Faster results for repeated queries

B Automatically creates indexes

C Deletes old data

D Improves network speed

Query caching stores results to quickly return them for repeated queries.

Which technique can help optimize a slow JOIN query?

A Using ORDER BY on all columns

B Using SELECT *

C Removing WHERE clauses

D Adding indexes on join columns

Indexes on join columns speed up matching rows between tables.

Explain how indexes improve query performance and when you should use them.

Think about how a book index helps find pages quickly.

Describe how the EXPLAIN statement helps in optimizing MySQL queries.

It's like a map of how the database will run your query.