题解：

select product_id,10 price from Products 
group by product_id
having min(change_date) > '2019-08-16'unionselect product_id,new_price price from Products
where (product_id,change_date) in (select product_id,max(change_date) from Productswhere change_date<='2019-08-16'group by product_id
)

题解：

select t1.person_name 
from Queue t1,Queue t2
where t1.turn>=t2.turn
group by t1.person_id
having sum(t2.weight)<=1000
order by t1.turn desc
limit 1

select t.person_name from (select turn,person_name, sum(weight) over(order by turn) sum_weightfrom Queue
) t
where t.sum_weight<=1000
order by t.sum_weight desc
limit 1

题解：

select "Low Salary" category,count(*) accounts_count from Accounts
where income<20000
union
select "Average Salary" category,count(*) accounts_count from Accounts
where income>=20000 and income<=50000
union
select "High Salary" category,count(*) accounts_count from Accounts
where income>50000