Database / Supabase Intermediate to Advanced Interview Questions
Why is EXPLAIN ANALYZE useful before optimizing a slow Supabase query?
EXPLAIN ANALYZE actually runs the query and reports Postgres's real execution plan — which indexes (if any) were used, how many rows were scanned at each step, and where the time was actually spent — rather than guessing based on how the query reads.
Without it, a common mistake is adding an index based on intuition that doesn't match what the planner actually does; a query might skip an existing index entirely because a function wraps the filtered column, or because the planner estimates a full table scan is cheaper for a small table. Reading the plan first turns index or query changes into an evidence-based decision instead of a guess, and re-running EXPLAIN ANALYZE after a change confirms whether it actually helped rather than assuming it did.
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