SQL Academy
Premium
Premium course
PostgreSQL
10 hours

SQL Query Optimization in PostgreSQL

Stop guessing why your queries are slow. In this course, you will learn how to read execution plans, effectively use indexes, and speed up queries by 100x+ through real-world examples.

  • Close 'this query is slow' tickets yourself — via EXPLAIN, indexes, statistics
  • Cut latency on slow production queries by 10–100×
  • Explain to your team why the planner picked this plan
12 lessons
Certificate upon completion
Course curriculum

This course is part of Premium — along with the other advanced courses, the AI assistant and certificates.

slow_query.sql
-- orders — 2.4M rows
SELECT * FROM orders
WHERE customer_id = 42;
Seq Scan on orders
4 280 ms
CREATE INDEX idx_orders_customer
ON orders (customer_id);
Index Scan
2.8 ms
⚡ 1,500× faster

What changes after the course

Now
After the course
A “query is slow” ticket goes to the DBA and sits for days
You read EXPLAIN ANALYZE and find the bottleneck yourself in minutes
Indexes get added by guesswork — “maybe it helps”
You design composite and partial indexes for the specific query
LIKE search brings the database down on big tables
You speed up text search with the right indexes and operators
OFFSET pagination gets slower with every page
You build keyset pagination and sorting without in-memory Sort

Course curriculum

Each lesson is short theory with runnable examples plus practice in the trainer with automatic checking.

01
About the Course: Why Optimization?
Learn why optimization is crucial and what problems it solves.
02
Anatomy of SQL Query: EXPLAIN and Indexes
Understand how the database executes a query and how indexes speed up this process.
03
Selectivity: why index doesn't work?
Understand when an index is useful and when the database will ignore it.
04
Composite Indexes
Learn to create multi-column indexes and consider column order.
05
SARGable: why functions kill indexes
Find out how functions and operators can 'kill' index performance.
06
Covering Indexes: reading data without the table
Optimize queries to read data only from the index, avoiding table access.
07
Text Search: how to speed up LIKE
Speed up text search with the right indexes and operators.
08
JOIN Optimization: why foreign keys slow down
Understand JOIN strategies and why foreign keys matter for performance.
09
Partial Indexes: diet for the database
Save space and speed up search by indexing only a subset of data.
10
Sorting
Optimize sorting to avoid expensive in-memory sort operations.
11
Pagination: why OFFSET kills performance
Implement fast pagination without using the slow OFFSET.
12
Performance Checklist
Let's review the key principles of query optimization.

How the learning works

01

Read a lesson with live examples

No-fluff theory: every query in a lesson can be run and tweaked right in your browser.

02

Solve exercises on a real database

You write SQL in the trainer and your answer is automatically checked against a real database. Nothing to install.

03

Stuck? The AI mentor helps

The built-in assistant points out what's wrong with your query and nudges you towards the solution without giving it away.

Who this course is for

Backend and fullstack developers

So that “the query is slow” tickets get closed by your commit instead of being escalated to a DBA.

Interview candidates

Indexes, EXPLAIN and query cost are among the most common database interview topics. This course covers them end to end.

Analysts and DBAs

So that heavy reporting queries stop eating up database resources and timing out dashboards.

You'll need solid SQL basics — SELECT, JOIN, GROUP BY. If you don't have them yet, start with the free course.

A certificate you can verify

Complete all lessons and receive a personalized course certificate. Attach it to your CV or LinkedIn profile.

A certificate you can verify
Your name and the course title
QR code and verification link

What learners say

Anna
Anna
After completing the course, I got promoted to data analyst. The course paid for itself in just one working day with my new salary!
Nikolay
Nikolay
Excellent presentation of the material! Very pleased with tasks from interviews at large IT companies.
Liza
Liza
The site is great! Tasks are interesting, UX is at a high level! Verification based on query results, not the query itself like on other sites.

One Premium — all courses at once

You're not buying a single course but the whole SQL Academy Premium: every advanced course and every trainer feature.

  • Access to advanced SQL courses
  • Unlimited hints from AI Assistant
  • Access to tasks from top company interviews
  • Access to reference solutions for tasks
  • Certificates proving your SQL knowledge
$ 36,90
6-month access, no auto-renewal

Secure card payment via Stripe. Access opens immediately after payment.

FAQ

Developers (Backend, Fullstack) and DBAs who want to write fast queries and confidently answer optimization questions in interviews — it's one of the most common topics.
No, all learning takes place in the browser, so no setup is required.
Yes, after completing every lesson in the course, you can get a personalized certificate.
Being comfortable with SELECT, JOIN and GROUP BY is enough — everything deeper is explained from scratch. If you're missing the basics, take the free course first.
All advanced courses, plus the AI assistant, interview tasks from top companies, reference solutions and certificates.
6 months from the moment of payment — more than enough to complete all the advanced courses.
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