Inspect the query plan with EXPLAIN ANALYZE to find sequential scans and missing indexes.
Guessing at optimizations wastes effort and can make things worse; the plan shows the real bottleneck.
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A slow query's cause — a sequential scan, a bad join order, a missing index — is invisible from the SQL text alone. EXPLAIN ANALYZE shows the planner's actual chosen plan and real row counts, so you optimize the real bottleneck instead of guessing.
-- Bad: add an index on a hunch and hope it helps
CREATE INDEX ON orders (status);-- Good: read the plan first, then act on what it shows
EXPLAIN ANALYZE
SELECT * FROM orders WHERE status = 'open' AND created_at > now() - interval '7 days';