SQL EXPLAIN

Ask Postgres to show you the plan before you spend any time guessing.

What & Why

Prefixing any query with EXPLAIN shows the planned execution tree without actually running the query — the fastest way to see how a query will be handled.

See How It Works

BUSINESS QUESTION

Inspect how PostgreSQL filters recent growth events for one event name.

id	user_id	event_name	created_at	properties
1001	101	signup	2024-01-15 09:12:00+00	{"source":"organic"}
1002	101	activated	2024-01-16 14:25:00+00	{"step":"workspace"}
1003	102	signup	2024-02-10 11:08:00+00	{"source":"paid"}
1004	103	report_viewed	2024-03-12 16:40:00+00	{"report":"retention"}

Read a representative EXPLAIN node field by fieldField 1 of 3

growth.events · event_name = 'signup' · created_at >= 2024-01-01

plan field	representative value	how to read it
node	Seq Scan on growth.events	one scan node for this small fixture
filter	event_name = 'signup' AND created_at >= 2024-01-01	predicate attached to the scan
estimated rows	planner dependent	cardinality estimate from statistics
cost	planner dependent	estimated work, not milliseconds

A small table may use one sequential-scan node; that plan choice is not automatically a problem.

EXAMPLE QUERY

EXPLAIN
SELECT
  user_id,
  event_name,
  created_at
FROM growth.events
WHERE event_name = 'signup'
  AND created_at >= TIMESTAMPTZ '2024-01-01 00:00:00+00';

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Advanced business practice