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-- Idempotent order creation (safe to retry) INSERT INTO orders (id, user_id, status) VALUES (UUID(), 1, "pending") ON DUPLICATE KEY UPDATE status = VALUES(status); -- Inventory reservation with rollback safety START TRANSACTION; UPDATE inventory SET reserved = reserved + 1, available = available - 1 WHERE product_id = 5 AND available >= 1; SELECT ROW_COUNT() INTO @updated; IF @updated = 0 THEN ROLLBACK; ELSE COMMIT; END IF;
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