SELECT bd.SENSOR_ID as sensorId, si.sensor_name AS sensorName, si.dam_id as damId, bd.WATER_LEVEL AS waterLevel, bd.WATER_TOP AS waterTop , bd.HOLE_DEPTH AS holeDepth, td.height-bd.WATER_TOP AS buryDepth FROM ( SELECT DAM_ID,SENSOR_ID, WATER_LEVEL,WATER_TOP, HOLE_DEPTH, ROW_NUMBER ( ) OVER ( PARTITION BY SENSOR_ID ORDER BY UPLOAD_TIME DESC ) AS RN FROM B_DAM_WATER_LEVEL ) bd LEFT JOIN sensor_info si ON bd.SENSOR_ID = si.sensor_id LEFT JOIN tailings_dam td ON bd.DAM_ID=td.dam_id WHERE bd.RN = 1 给我优化一下查询速度

可以尝试以下几种优化方法：

1. 添加索引：对 B_DAM_WATER_LEVEL 表中的 SENSOR_ID 和 UPLOAD_TIME 字段添加联合索引，对 SENSOR_INFO 表中的 SENSOR_ID 字段添加索引，对 TAILINGS_DAM 表中的 DAM_ID 字段添加索引。

CREATE INDEX idx_sensor_upload ON B_DAM_WATER_LEVEL (SENSOR_ID, UPLOAD_TIME);
CREATE INDEX idx_sensor ON SENSOR_INFO (SENSOR_ID);
CREATE INDEX idx_dam ON TAILINGS_DAM (DAM_ID);

2. 使用 EXISTS 子查询代替 LEFT JOIN：将 LEFT JOIN 改为 EXISTS 子查询，可以避免重复数据的产生，从而提高查询效率。

SELECT bd.SENSOR_ID as sensorId, si.sensor_name AS sensorName, si.dam_id as damId, bd.WATER_LEVEL AS waterLevel, bd.WATER_TOP AS waterTop , bd.HOLE_DEPTH AS holeDepth, td.height-bd.WATER_TOP AS buryDepth         
FROM ( 
    SELECT DAM_ID,SENSOR_ID, WATER_LEVEL,WATER_TOP, HOLE_DEPTH 
    FROM B_DAM_WATER_LEVEL bd1 
    WHERE bd1.RN = 1 
    AND EXISTS (
        SELECT 1 
        FROM B_DAM_WATER_LEVEL bd2 
        WHERE bd2.SENSOR_ID = bd1.SENSOR_ID 
        AND bd2.UPLOAD_TIME > bd1.UPLOAD_TIME
    )
) bd         
WHERE bd.SENSOR_ID = si.sensor_id         
AND bd.DAM_ID = td.dam_id;

3. 减少 SELECT 中的字段数量：只查询需要的字段，避免不必要的开销。

SELECT bd.SENSOR_ID as sensorId, si.sensor_name AS sensorName, si.dam_id as damId, bd.WATER_LEVEL AS waterLevel, bd.WATER_TOP AS waterTop , bd.HOLE_DEPTH AS holeDepth, td.height-bd.WATER_TOP AS buryDepth         
FROM ( 
    SELECT DAM_ID,SENSOR_ID, WATER_LEVEL,WATER_TOP, HOLE_DEPTH 
    FROM B_DAM_WATER_LEVEL bd1 
    WHERE bd1.RN = 1 
    AND EXISTS (
        SELECT 1 
        FROM B_DAM_WATER_LEVEL bd2 
        WHERE bd2.SENSOR_ID = bd1.SENSOR_ID 
        AND bd2.UPLOAD_TIME > bd1.UPLOAD_TIME
    )
) bd         
WHERE bd.SENSOR_ID = si.sensor_id         
AND bd.DAM_ID = td.dam_id;