sql优化：如何优化此查询？
原查询如下：
select
es.id,
es.station_name,
es.province,
es.city,
es.district,
es.detailed,
( select count(*) from air_conditioner_equipment where station_id = es.id ) as air_conditioning_count,
( select sum( cold_power ) from air_conditioner_equipment where station_id = es.id) as cold_power_total,
( select sum( hot_power) from air_conditioner_equipment where station_id = es.id) as hot_power_total,
es.create_time,
es.state
from
energy_station es
left join user_station us on us.station_id = es.id
left join user_info u on u.id = us.user_id优化建议：
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- 为air_conditioner_equipment表的station_id列添加索引。
通过添加索引，mysql可以更有效地查找数据，从而提高查询速度。
优化后的查询：
SELECT
es.id,
es.station_name,
es.province,
es.city,
es.district,
es.detailed,
SUM(ace.air_conditioning_count) AS air_conditioning_count,
SUM(ace.cold_power) AS cold_power_total,
SUM(ace.hot_power) AS hot_power_total,
es.create_time,
es.state
FROM energy_station es
LEFT JOIN user_station us ON us.station_id = es.id
LEFT JOIN user_info u ON u.id = us.user_id
LEFT JOIN (
SELECT station_id, COUNT(*) as air_conditioning_count, SUM(cold_power) as cold_power, SUM(hot_power) as hot_power
FROM air_conditioner_equipment
GROUP BY station_id
) ace ON ace.station_id = es.id
GROUP BY es.id; 
