Same query can be written with JOIN or subquery. Choice affects performance and readability. Understanding trade-offs is essential for query optimization.

Query Optimization Decision

Development team needs to choose between JOIN and subquery approaches for customer filtering queries.

Performance testing shows EXISTS subquery outperforms JOIN with DISTINCT

-- Optimized approach using EXISTS

SELECT c.customer_name, c.email, c.registration_date

FROM customers c

WHERE EXISTS (

SELECT 1 FROM orders o

WHERE o.customer_id = c.customer_id

AND o.order_date >= CURRENT_DATE - INTERVAL 90 DAY

AND o.status = 'completed'

);

Improved query performance by 40% compared to JOIN approach. Better user experience in customer management system.

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