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 |
+----+
分析：意思就是在Weather表中，写一个SQL查询与前一天相比温度更高的日期对应的ID。
代码：

# Write your MySQL query statement below
SELECT w1.Id 
FROM Weather w1 JOIN Weather w2 ON TO_DAYS(w1.Date)=TO_DAYS(w2.Date)+1 And w1.Temperature>w2.Temperature; 

　其中，TO_DAYS(date) 给定一个日期date, 返回一个天数 (从年份0开始的天数 )　

其他解法：

SELECT w1.Id FROM Weather w1, Weather w2 WHERE dateDiff(w1.Date,w2.Date) = 1 AND w1.Temperature > w2.Temperature;

　　其中，dateDiff() 函数返回两个日期之间的天数。

还有这样的方式：

 date_add(w1.date,interval 1 day)=w2.date

w2.Date = DATE_SUB(w1.Date, INTERVAL 1 DAY)

leetcode：Rising Temperature

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原文地址：http://www.cnblogs.com/carsonzhu/p/4620943.html