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如何优化包含子查询的复杂SQL语句?


如何优化包含子查询的复杂SQL语句?

如何优化复杂sql语句

sql语句如下:

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
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优化方法

  1. 添加索引

为表air_conditioner_equipment的字段station_id添加索引,可以加快根据该字段进行查询的速度。

  1. 使用子查询优化

优化后sql语句如下:

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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优化后的sql语句使用子查询ace来预先计算所需的聚合值,然后再使用left join将其与主表连接。这样可以减少需要进行的子查询数量,从而提高查询效率。

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