Guided Notes

Writing Efficient Queries

Select only what you need, read less data, and avoid N:N joins.

Why efficiency matters

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On small tables every query is fast. On big data, an inefficient query can take minutes β€” and in cloud warehouses that bill by bytes scanned, it costs real money.

BigQuery shows how much data a query will process before you run it, and other databases offer EXPLAIN plans. Measure before and after instead of guessing.

Three habits make most of the difference.

← Indexes