sql语句，部分正确，求解答

select Pid
from orders
group by Pid
having sum(QTY)=(
    select sum(QTY)
    from orders
    group by Pid    
    order by sum(QTY) limit 1
)

是按照订单量还是订购数据最多？订单量最多用count，而且要指定desc降序排列
按照订单量最多用下面的

select Pid
from orders
group by Pid
having count(OrdNo)=(
    select count(OrdNo)
    from orders
    group by Pid    
    order by count(OrdNo) desc limit 1
)

按照订购数量，在原来基础上加个desc

select Pid
from orders
group by Pid
having sum(QTY)=(
    select sum(QTY)
    from orders
    group by Pid    
    order by sum(QTY) desc limit 1
)

根据Pid进行分组，并且根据sum(QTY)进行排序，取第一条记录

SELECT Pid
FROM orders
GROUP BY Pid
ORDER BY sum(QTY) DESC
LIMIT 1;

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