leetcode-Rising Temperature
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Given a
Weather
table, write a SQL query to find all dates' Ids with higher temperature compared to its previous (yesterday's) dates.+---------+------------+------------------+| Id(INT) | Date(DATE) | Temperature(INT) |+---------+------------+------------------+| 1 | 2015-01-01 | 10 || 2 | 2015-01-02 | 25 || 3 | 2015-01-03 | 20 || 4 | 2015-01-04 | 30 |+---------+------------+------------------+
For example, return the following Ids for the above Weather table:
+----+| Id |+----+| 2 || 4 |+----+
思路:
(注:to_days(datex)将datex转换成int可进行大小比较的类型)
思路一:
这是最基本最首先应该想到的思路:从一个表中选择一些special的元组,我们要通过where来对其拥有的属性进行筛选,符合条件的才能够选择出来。在这题里面就是选出“Temperature”这个属性值大于
“Date”属性值比自己“Date”属性值小1的那个元组的“Temperature”属性值。然后进行一次嵌套选择即OK
思路二:
这是角度和思路一稍微不同的一种解法,我的理解是这种解法是通过“空间”上的复杂度来避免了嵌套select带来的时间上的复杂度,至于二者究竟谁更快现在还不太清楚。
思路一:
select a.Id from Weather as a where a.Temperature > (select b.Temperature from Weather as b where to_days(b.Date)+1 = to_days(a.Date))
思路二:
select b.Idfrom Weather as a,Weather as bwhere TO_DAYS(a.Date) +1 = TO_DAYS(b.Date) and a.Temperature < b.Temperature
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