如何优化查询以提高性能？
以下是一条查询语句：
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.statefrom energy_station esleft join user_station us on us.station_id = es.idleft join user_info u on u.id = us.user_id
针对此查询，可以通过以下方法进行优化：
添加索引
查询中频繁连接的字段station_id未添加索引，这会导致查询性能低下。为station_id字段添加索引可以显着提高查询速度。
使用子查询优化
查询中包含多个子查询，这会导致查询执行效率低下。可以使用连接子查询的方式来优化查询：
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.stateFROM energy_station esLEFT JOIN user_station us ON us.station_id = es.idLEFT JOIN user_info u ON u.id = us.user_idLEFT 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.idGROUP BY es.id;
通过连接子查询，可以将多个子查询合并为一个，从而提高查询效率。
以上就是如何优化包含子查询的 SQL 查询以提高性能？的详细内容，更多请关注创想鸟其它相关文章！
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