EXPLAIN | PostgreSQL Tutorial

EXPLAIN in Performance helps you write SQL that is easier to test, review, and operate at scale.

Introduction to EXPLAIN

Use EXPLAIN to inspect query behavior and apply targeted optimizations.

Commonly paired with: SELECT, FROM, WHERE, ORDER BY.

Practical examples with EXPLAIN in PostgreSQL

Reference pattern: start from canonical syntax and keep it explicit.

EXPLAIN
SELECT *
FROM orders
WHERE customer_id = 42
ORDER BY placed_at DESC
LIMIT 20;

Production-style scenario: apply the same concept to realistic application data.

EXPLAIN (ANALYZE, BUFFERS)
SELECT o.order_id, o.total_amount
FROM orders o
WHERE o.customer_id = 42
ORDER BY o.placed_at DESC
LIMIT 25;

Additional example: use a variation to validate behavior and edge cases.

EXPLAIN (ANALYZE, BUFFERS)
SELECT customer_id, SUM(total_amount)
FROM orders
WHERE placed_at >= now() - interval '30 days'
GROUP BY customer_id
ORDER BY SUM(total_amount) DESC
LIMIT 20;

Production tips

Prefer explicit column lists and deterministic ordering when results feed APIs or batch jobs.
Validate plans with EXPLAIN before adding indexes, then re-check after schema changes.
Keep DDL, data backfills, and cleanups in transactions when possible to avoid partial state.
Use isolated environments for risky changes so query tuning and schema experiments stay safe.

Vela workflow tip

Test this pattern in an isolated branch database, share the result with your team, and promote only after query plans and row counts look correct.

Reference: PostgreSQL official documentation.