设计到的表:product、pc、laptop
select avg(price) as avg_price
from (select model,price from pcunionselect model,price from laptop
)as a
where model in (select model from productwhere maker='D'
)
设计到的表:product、pc、laptop
select avg(price) as avg_price
from (select model,price from pcunionselect model,price from laptop
)as a
where model in (select model from productwhere maker='D'
)