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：
- 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;
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