Intermediate Topic 32 of 51 Databases
Query Execution Plans
Operator trees showing how a query will run.
How it works
EXPLAIN shows operators (seq scan, index scan, hash join, sort) with estimated and actual costs and row counts. Compare estimates with reality to find problems.
Where it is used
Tuning queries.
Common pitfall
A sequential scan is not always bad for small tables.
Where it fits in the course
Query Execution Plans is topic 32 of 51 in Databases, rated Intermediate. It follows Query Optimization. The next topic is Window Functions.
Practice and explore
- Open the interactive lesson, with a mini quiz.
- Take the Databases quiz.
How to study this topic
- Read the explanation above and restate the definition in your own words.
- Open the interactive lesson and answer its mini quiz.
- Read the common pitfall, then write a short example that avoids it.
- Check your understanding in the Databases quiz, and revisit the topic if you miss a question.
Frequently asked questions
What is Query Execution Plans?
Operator trees showing how a query will run. It belongs to Databases and is an intermediate-level topic.
Where do people use Query Execution Plans?
Tuning queries.
What is the most common mistake with Query Execution Plans?
A sequential scan is not always bad for small tables.
What should I learn before this topic?
Start with Query Optimization, the topic just before it in Databases.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Databases quiz.
Is Query Execution Plans hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Query Execution Plans?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Query Execution Plans?
Query Optimization, Window Functions, Stored Procedures and Triggers are closely connected. The full list is in the related topics section of this page.
What should I study after Query Execution Plans?
Continue with Window Functions, the next topic in Databases.
Related topics
- Query Optimization (Databases)
- Window Functions (Databases)
- Stored Procedures and Triggers (Databases)
- Common Table Expressions (Databases)
- Out-of-Order Execution (Computer Architecture & Logic)
- Speculative Execution (Computer Architecture & Logic)
- Trusted Execution Environments (Security & Cryptography)