`EXPLAIN ANALYZE` shows the difference between what PostgreSQL planned and what actually ran

PostgreSQL's query planner estimates row counts before running a query. `EXPLAIN` shows the plan and estimates; `EXPLAIN ANALYZE` actually runs the query and shows both estimated and actual row counts. When the planner estimates 10 rows but 100,000 rows actually come back, it has chosen a nested loop where a hash join would have been far better. This mismatch usually means stale table statistics: running `ANALYZE tablename` lets the planner re-sample and produce better estimates.

-- I run EXPLAIN ANALYZE to see estimated vs actual row counts
EXPLAIN (ANALYZE, BUFFERS, FORMAT TEXT)
SELECT u.name, COUNT(o.id) as order_count
FROM users u
JOIN orders o ON o.user_id = u.id
WHERE u.created_at > '2026-01-01'
GROUP BY u.id;

-- Look for: rows=X (estimated) vs actual rows=Y
-- Large gaps mean stale statistics
-- Also look at: Seq Scan vs Index Scan choices

-- Fix stale statistics
ANALYZE users;
ANALYZE orders;