Leekno - Rising Temperature

Hello everyone, I am Kongkong star. This article will take you to understand a simple sql practice question.

---

foreword

---

1. Topic: 197. Rising temperature

Table: Weather

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| recordDate    | date    |
| temperature   | int     |
+---------------+---------+

id is the primary key of this table
which contains temperature information for a specific date

Write a SQL query to find the id's of all dates with a higher temperature than the previous (yesterday's) date.
The returned results do not require order.
The query result format is as follows.

输入：
Weather 表：
+----+------------+-------------+
| id | recordDate | Temperature |
+----+------------+-------------+
| 1  | 2015-01-01 | 10          |
| 2  | 2015-01-02 | 25          |
| 3  | 2015-01-03 | 20          |
| 4  | 2015-01-04 | 30          |
+----+------------+-------------+
输出：
+----+
| id |
+----+
| 2  |
| 4  |
+----+

Explanation:
The temperature on 2015-01-02 was higher than the previous day (10 -> 25)
The temperature on 2015-01-04 was higher than the previous day (20 -> 30)

Two, problem solving

1. Correct demonstration①

Submit SQL

select u2.id from Weather u1
left join Weather u2 
on DATE_ADD(u1.recordDate,INTERVAL 1 DAY)=u2.recordDate
where u2.Temperature>u1.Temperature;

operation result

2. Correct demonstration②

Submit SQL

select u2.id from Weather u1,Weather u2 
where DATE_SUB(u2.recordDate,INTERVAL 1 DAY)=u1.recordDate
and u2.Temperature>u1.Temperature;

operation result

3. Demonstrate correctly③

Submit SQL

select id from Weather u1
where exists (
    select 1 from Weather u2 
    where DATE_ADD(u2.recordDate,INTERVAL 1 DAY)=u1.recordDate 
    and u1.Temperature>u2.Temperature
)

operation result

4. Correct demonstration④

Submit SQL

select u2.id from Weather u1
join Weather u2 
on DATEDIFF(u2.recordDate,u1.recordDate)=1
where u2.Temperature>u1.Temperature;

operation result

5. Other

---

Summarize

DATE_ADDThe (date,INTERVAL expr type) function returns the date with the INTERVAL time interval added to date.
DATE_SUBThe (date,INTERVAL expr type) function returns the date with the INTERVAL time interval subtracted from date.
DATEDIFFThe (date1,date2) function calculates the number of days between two dates.