Date To days

# Write your MySQL query statement below
SELECT wt1.Id AS Id
FROM Weather wt1, Weather wt2
WHERE wt1.Temperature > wt2.Temperature AND 
      TO_DAYS(wt1.DATE) - TO_DAYS(wt2.DATE) = 1

586. Customer Placing the Largest Number of Orders

select customer_number from orders
group by customer_number
order by count(*) desc limit 1;

Group By

182. Duplicate Emails

重复自己的Table

180. Consecutive Numbers

# Write your MySQL query statement below
Select DISTINCT l1.Num AS ConsecutiveNums  from Logs l1, Logs l2, Logs l3
where l1.Id = l2.Id - 1 and l2.Id = l3.Id - 1 
and l1.Num = l2.Num and l2.Num = l3.Num

Top K问题

Delete

196. Delete Duplicate Emails