标签：ima where 换算 建表 etc engine round ted drop
给定一个Weather表，编写一个SQL查询来查找与之前(昨天的)日期相比温度更高的所有日期的id。
创建表和数据：
-- ---------------------------- -- Table structure for `weather` -- ---------------------------- DROP TABLE IF EXISTS `weather`; CREATE TABLE `weather` ( `Id` int(11) DEFAULT NULL, `RecordDate` date DEFAULT NULL, `Temperature` int(11) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4; -- ---------------------------- -- Records of weather -- ---------------------------- INSERT INTO `weather` VALUES (‘1‘,‘2015-01-01‘, ‘10‘); INSERT INTO `weather` VALUES (‘2‘,‘2015-01-02‘, ‘25‘); INSERT INTO `weather` VALUES (‘3‘,‘2015-01-03‘, ‘20‘); INSERT INTO `weather` VALUES (‘4‘,‘2015-01-04‘, ‘30‘);
解法：
1.思路简单。表自连接，找出温度比前一天高的行。
问题的关键是确定日期的前一天。
日期函数： DATEDIFF(date1,date2) ，返回date1与date2之间相差的天数。
SELECT W1.Id FROM weather AS W1 JOIN weather AS W2 ON (DATEDIFF(W1.RecordDate,W2.RecordDate) = 1 AND W1.Temperature > W2.Temperature)
2.同样，函数： TIMESTAMPDIFF(unit,begin,end)，返回begin与end之间相差多少个unit。unit为DAY时，即为相差“天”。
SELECT W2.Id FROM weather AS W1 JOIN weather AS W2 ON (TIMESTAMPDIFF(DAY,W1.RecordDate,W2.RecordDate) = 1 AND W1.Temperature < W2.Temperature);
TO_DAYS函数，用来将日期换算成天数
SELECT w1.Id FROM Weather w1, Weather w2 WHERE w1.Temperature > w2.Temperature AND TO_DAYS(w1.RecordDate)=TO_DAYS(w2.RecordDate) + 1;
使用Subdate函数，来实现日期减1
SELECT w1.Id FROM Weather w1, Weather w2 WHERE w1.Temperature > w2.Temperature AND SUBDATE(w1.RecordDate, 1) = w2.RecordDate;
leetcode197 上升的温度 Rising Temperature
标签：ima where 换算 建表 etc engine round ted drop
原文地址：https://www.cnblogs.com/forever-fortunate/p/11723358.html
