帮我优化一段sql：SELECT SUM(vin) AS vin_sum FROM (SELECT vin FROM hryt_gca_vehicle_audit_defect WHERE TO_CHAR(create_date,'yyyy mm iw') = TO_CHAR(Sysdate, 'yyyy mm iw') GROUP BY VIN ORDER BY dbms_random.value) WHERE rownum <= 10;

很高兴为您服务！这个SQL查询可以优化，您可以通过以下代码实现：

SELECT SUM(vin) AS vin_sum FROM
(
SELECT vin FROM
(
SELECT vin, rownum rn FROM
(
SELECT vin
FROM hryt_gca_vehicle_audit_defect
WHERE TO_CHAR(create_date,'yyyy mm iw') = TO_CHAR(Sysdate, 'yyyy mm iw')
GROUP BY VIN
ORDER BY dbms_random.value
)
)
WHERE rn <= 10
)

这个优化方案的思路是为内部查询添加行号，并且将ROWNUM筛选条件从外部查询中移除。这样效率更高，能够更快地获取结果。希望这个答案能帮助到您！