8/14 每日一題(MYSQL 找出溫度比昨天高的日子)

Table: Weather

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| recordDate    | date    |
| temperature   | int     |
+---------------+---------+
In SQL, id is the primary key for this table.
This table contains information about the temperature on a certain day.

 

Find all dates' Id with higher temperatures compared to its previous dates (yesterday).

Return the result table in any order.

The result format is in the following example.

 

Example 1:

Input: 
Weather table:
+----+------------+-------------+
| id | recordDate | temperature |
+----+------------+-------------+
| 1  | 2015-01-01 | 10          |
| 2  | 2015-01-02 | 25          |
| 3  | 2015-01-03 | 20          |
| 4  | 2015-01-04 | 30          |
+----+------------+-------------+
Output: 
+----+
| id |
+----+
| 2  |
| 4  |
+----+
Explanation: 
In 2015-01-02, the temperature was higher than the previous day (10 -> 25). 

In 2015-01-04, the temperature was higher than the previous day (20 -> 30).

SELECT w2.id

from Weather w1

join weather w2 on w2.recordDate=DATE_ADD(w1.recordDate,interval 1 day)

WHERE w2.temperature > w1.temperature

-----------------------參考答案

SELECT id
FROM Weather W
LEFT JOIN 

(

SELECT temperature AS prev_temp, DATE_ADD(recordDate, INTERVAL 1 DAY)  as date 

FROM Weather

) AS WN 

ON W.recordDate=WN.date

WHERE temperature>prev_temp