BQ Query Rewrite Strategies
Query Rewrite Strategies Used by Top Tech Companies
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5 min•Feb 28, 2026
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? 1. Two-Phase Aggregation
Instead of:
SELECT user_id, COUNT(DISTINCT session_id)
FROM events
GROUP BY user_id
FROM events
GROUP BY user_id
Rewrite:
Pre-aggregate per day
Aggregate per user
Reduces shuffle width drastically.
? 2. Approximate Functions
Use:
APPROX_COUNT_DISTINCT
HLL
Reduces shuffle memory pressure.
? 3. Join Elimination via Denormalization
Instead of 5-way joins:
Create wide fact table
Update via pipeline
Compute moves to ingestion time.
? 4. Filter Before Join
Always reduce dataset size before joining.
? 5. Break Monolith Queries
Large 200-line SQL → 3 materialized steps.
Reduces:
Reattempts
Shuffle spill
Memory pressure
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