PostgreSQL Foundations·A database you can operate

Indexes and query plans

An index trades write cost and storage for faster reads—when it matches the query.

Intermediate 15 min read Lesson 9 of 300 Challenge included

What you will be able to do

Read the plan from the innermost node outward.
Compare estimated rows with actual rows; large gaps signal stale statistics.
Use CREATE INDEX CONCURRENTLY in production.

In plain English

EXPLAIN ANALYZE shows what the planner actually did. A B-tree index helps equality and range predicates; a composite index follows the leftmost-prefix rule. Do not index every column; write cost and bloat add up.

indexes.sqlSQL

create index lessons_course_idx
  on lessons (course_slug, minutes desc);

explain analyze
select slug, title, minutes
from lessons
where course_slug = 'html'
  and minutes >= 10
order by minutes desc
limit 5;

Your turn

Index a lookup

Medium

Create an index on lessons(course_slug, minutes desc) and explain why it helps a filtered, ordered query.

SQL · starter

create index lessons_idx on lessons ();

Check your understanding before moving on.

Knowledge checkQuestion 1

What does EXPLAIN ANALYZE do that EXPLAIN does not?

Select an answer to continue

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