Merge pull request #74 from iamAntimPal/Branch-1

Branch 1

Author: iamAntimPal

LeetCode SQL 50 Solution/197. Rising Temperature/Rising Temperature.py

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+
+# **197. Rising Temperature**
+
+## **Problem Statement**
+You are given a table called `Weather`, which contains daily temperature records.
+
+### **Weather Table**
+```
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| id            | int     |
+| recordDate    | date    |
+| temperature   | int     |
++---------------+---------+
+```
+- `id` is the **primary key**.
+- Each row contains:
+  - `recordDate`: The **date** of the temperature record.
+  - `temperature`: The **temperature recorded** on that date.
+
+### **Task:**
+Find all `id`s where the **temperature** is **higher** than the **previous day's temperature**.
+
+---
+
+## **Example 1:**
+### **Input:**
+#### **Weather Table**
+```
++----+------------+-------------+
+| id | recordDate | temperature |
++----+------------+-------------+
+| 1  | 2024-08-01 | 30          |
+| 2  | 2024-08-02 | 32          |
+| 3  | 2024-08-03 | 31          |
+| 4  | 2024-08-04 | 35          |
+| 5  | 2024-08-05 | 36          |
++----+------------+-------------+
+```
+### **Output:**
+```
++----+
+| id |
++----+
+| 2  |
+| 4  |
+| 5  |
++----+
+```
+### **Explanation:**
+- `id = 2`: `32 > 30` (08-02 > 08-01 ✅)
+- `id = 3`: `31 < 32` (Skipped ❌)
+- `id = 4`: `35 > 31` (08-04 > 08-03 ✅)
+- `id = 5`: `36 > 35` (08-05 > 08-04 ✅)
+
+---
+
+## **Solution Approaches**
+
+### **SQL Solution (Using `LAG()` Window Function)**
+```sql
+WITH PreviousWeatherData AS
+(
+    SELECT 
+        id,
+        recordDate,
+        temperature, 
+        LAG(temperature, 1) OVER (ORDER BY recordDate) AS PreviousTemperature,
+        LAG(recordDate, 1) OVER (ORDER BY recordDate) AS PreviousRecordDate
+    FROM 
+        Weather
+)
+SELECT 
+    id 
+FROM 
+    PreviousWeatherData
+WHERE 
+    temperature > PreviousTemperature
+AND 
+    recordDate = DATE_ADD(PreviousRecordDate, INTERVAL 1 DAY);
+```
+**Explanation:**
+- We use `LAG()` to fetch:
+  - The **previous day's temperature**.
+  - The **previous day's date**.
+- The `WHERE` clause filters rows where:
+  - The **temperature is higher than the previous day**.
+  - The **date difference is exactly 1 day**.
+
+---
+
+### **SQL Solution (Using Self Join)**
+```sql
+SELECT w1.id
+FROM Weather w1
+JOIN Weather w2
+ON DATEDIFF(w1.recordDate, w2.recordDate) = 1
+AND w1.temperature > w2.temperature;
+```
+**Explanation:**
+- We **self-join** the `Weather` table.
+- The condition `DATEDIFF(w1.recordDate, w2.recordDate) = 1` ensures:
+  - We are comparing **consecutive days**.
+- The condition `w1.temperature > w2.temperature` ensures:
+  - We select days where the **temperature increased**.
+
+---
+
+### **Pandas Solution**
+```python
+import pandas as pd
+
+def rising_temperature(weather: pd.DataFrame) -> pd.DataFrame:
+    weather.sort_values(by="recordDate", inplace=True)
+    weather["PreviousTemp"] = weather["temperature"].shift(1)
+    weather["PreviousDate"] = weather["recordDate"].shift(1)
+    
+    result = weather[
+        (weather["temperature"] > weather["PreviousTemp"]) &
+        ((weather["recordDate"] - weather["PreviousDate"]).dt.days == 1)
+    ]
+    
+    return result[["id"]]
+```
+**Explanation:**
+- We **sort** by `recordDate`.
+- We **shift** the temperature and date to get the previous day's values.
+- We **filter** where:
+  - Temperature **increased**.
+  - Date difference is **1 day**.
+
+---
+
+## **File Structure**
+```
+📂 LeetCode197
+│── 📜 problem_statement.md
+│── 📜 sql_lag_solution.sql
+│── 📜 sql_self_join_solution.sql
+│── 📜 pandas_solution.py
+│── 📜 README.md
+```
+- `problem_statement.md` → Contains the problem description.
+- `sql_lag_solution.sql` → Contains the SQL solution using **LAG()**.
+- `sql_self_join_solution.sql` → Contains the SQL solution using **Self Join**.
+- `pandas_solution.py` → Contains the Pandas solution.
+- `README.md` → Provides an overview of the problem and solutions.
+
+---
+
+## **Useful Links**
+- [LeetCode Problem 197](https://leetcode.com/problems/rising-temperature/)
+- [SQL LAG() Function](https://www.w3schools.com/sql/sql_ref_window_functions.asp)
+- [SQL JOIN](https://www.w3schools.com/sql/sql_join.asp)
+- [Pandas shift()](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.shift.html)
+