如何優化包含子查詢的 SQL 查詢以提高性能?

如何優化包含子查詢的 SQL 查詢以提高性能?

如何優化查詢以提高性能?

以下是一條查詢語句:

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.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

針對此查詢,可以通過以下方法進行優化:

添加索引

查詢中頻繁連接的字段station_id未添加索引,這會導致查詢性能低下。為station_id字段添加索引可以顯著提高查詢速度。

使用子查詢優化

查詢中包含多個子查詢,這會導致查詢執行效率低下??梢允褂眠B接子查詢的方式來優化查詢:

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;

通過連接子查詢,可以將多個子查詢合并為一個,從而提高查詢效率。

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