case coalesce(t3.volume,'')
when '' then t2.volume
else t3.volume
end as transaction_volume
,case coalesce(t3.area,'')
when '' then t2.area
else t3.area
end as transaction_area
,case coalesce(t3.sets,'')
when '' then t2.sets
else t3.sets
end as transaction_sets
,case when coalesce(t2.mdm_building_id,'') != '' then 0
when coalesce(t3.mdm_building_id,'') != '' then 1
end as received_flag
必须用相同得大小啊