給定一個Weather表，寫一條SQL語句返回所有溫度比前一天高的資料的Id

+---------+------------------+------------------+
| Id(INT) | RecordDate(DATE) | Temperature(INT) |
+---------+------------------+------------------+
|       1 |       2015-01-01 |               10 |
|       2 |       2015-01-02 |               25 |
|       3 |       2015-01-03 |               20 |
|       4 |       2015-01-04 |               30 |
+---------+------------------+------------------+
 

例如，上面的天氣表返回下面的Id結果

+----+
| Id |
+----+
|  2 |
|  4 |
+----+

DATEDIFF() 函式返回兩個日期之間的天數。

由於Id的排列未必是按順序的，所以要找前一天就得根據日期來找，可以使用MySQL的函式Datadiff來計算兩個日期的差值。限制條件是溫度高且日期差1

SELECT W1.Id 
FROM Weather AS W1, Weather AS W2
WHERE DATEDIFF(W1.RecordDate, W2.RecordDate)=1 AND W1.Temperature>W2.Temperature
 

2：利用DATA_SUB()方法

DATE_SUB() 函式從日期減去指定的時間間隔

SELECT W1.Id 
FROM Weather AS W1, Weather AS W2
WHERE DATE_SUB(W1.RecordDate, INTERVAL 1 DAY)=W2.RecordDate AND W1.Temperature>W2.Temperature

3：利用DATA_ADD()方法

SELECT W1.Id 
FROM Weather AS W1, Weather AS W2
WHERE W1.RecordDate=DATE_ADD(W2.RecordDate, INTERVAL 1 DAY) AND W1.Temperature>W2.Temperature
 

to_days(date) -將日期型別轉為數字型別

from_days(date)-將天數轉為日期

SELECT W1.Id 
FROM Weather AS W1, Weather AS W2
WHERE TO_DAYS(W1.RecordDate)-TO_DAYS(W2.RecordDate)=1 AND W1.Temperature>W2.Temperature