SELECT avg(mw) as av FROM Meter_reading WHERE hierarchy_id in(1,2) 并联合所有 SELECT avg(elec) as av FROM Meter_reading WHERE hierarchy_id in(1,2)(示例)
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SELECT avg(mw) as av FROM Meter_reading WHERE hierarchy_id in(1,2) 并联合所有 SELECT avg(elec) as av FROM Meter_reading WHERE hierarchy_id in(1,2)(示例)