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Author: iamAntimPal

LeetCode SQL 50 Solution/619. Biggest Single Number/619. Biggest Single Number.py

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+Below is the structured README.md snippet for **LeetCode 619: Biggest Single Number**, including the problem statement, example, solution approaches (SQL and Pandas), file structure, and useful links.
+
+---
+
+# **619. Biggest Single Number**
+
+## **Problem Statement**
+You are given a table `MyNumbers` that contains integers, which may include duplicates.
+
+### **MyNumbers Table**
+```
++-------------+------+
+| Column Name | Type |
++-------------+------+
+| num         | int  |
++-------------+------+
+```
+- There is **no primary key** for this table.
+- Each row contains an integer.
+
+### **Task:**
+A **single number** is a number that appears **only once** in the `MyNumbers` table.  
+Find the **largest single number**. If there is no single number, report `null`.
+
+---
+
+## **Example 1:**
+
+### **Input:**
+```
+MyNumbers table:
++-----+
+| num |
++-----+
+| 8   |
+| 8   |
+| 3   |
+| 3   |
+| 1   |
+| 4   |
+| 5   |
+| 6   |
++-----+
+```
+
+### **Output:**
+```
++-----+
+| num |
++-----+
+| 6   |
++-----+
+```
+
+### **Explanation:**
+- The single numbers (appear exactly once) are: **1, 4, 5, 6**.
+- The largest among these is **6**.
+
+---
+
+## **Example 2:**
+
+### **Input:**
+```
+MyNumbers table:
++-----+
+| num |
++-----+
+| 8   |
+| 8   |
+| 7   |
+| 7   |
+| 3   |
+| 3   |
+| 3   |
++-----+
+```
+
+### **Output:**
+```
++------+
+| num  |
++------+
+| null |
++------+
+```
+
+### **Explanation:**
+- There are no single numbers (all numbers appear more than once), so the result is `null`.
+
+---
+
+## **Solution Approaches**
+
+### **SQL Solution**
+```sql
+SELECT MAX(num) AS num
+FROM (
+    SELECT num
+    FROM MyNumbers
+    GROUP BY num
+    HAVING COUNT(num) = 1
+) AS unique_numbers;
+```
+**Explanation:**
+- The subquery groups by `num` and filters to include only those numbers that appear exactly once (`HAVING COUNT(num) = 1`).
+- The outer query returns the maximum value from these unique numbers.
+- If no unique number exists, `MAX(num)` returns `null`.
+
+---
+
+### **Pandas Solution**
+```python
+import pandas as pd
+
+def biggest_single_number(my_numbers: pd.DataFrame) -> pd.DataFrame:
+    # Group by 'num' and filter those numbers that appear exactly once
+    unique_numbers = my_numbers.groupby('num').filter(lambda group: len(group) == 1)
+    
+    # Determine the largest single number, if any
+    if unique_numbers.empty:
+        result = None
+    else:
+        result = unique_numbers['num'].max()
+    
+    return pd.DataFrame({'num': [result]})
+
+# Example usage:
+# df = pd.DataFrame({'num': [8, 8, 3, 3, 1, 4, 5, 6]})
+# print(biggest_single_number(df))
+```
+**Explanation:**
+- The solution groups the DataFrame by `num` and filters groups where the number appears exactly once.
+- It then calculates the maximum from the filtered DataFrame.
+- If there are no unique numbers, it returns `None`.
+
+---
+
+## **File Structure**
+```
+LeetCode619/
+├── problem_statement.md       # Contains the problem description and constraints.
+├── sql_solution.sql           # Contains the SQL solution.
+├── pandas_solution.py         # Contains the Pandas solution for Python users.
+├── README.md                  # Overview of the problem and available solutions.
+```
+
+---
+
+## **Useful Links**
+- [LeetCode Problem 619](https://leetcode.com/problems/biggest-single-number/)
+- [SQL GROUP BY and HAVING Clause](https://www.w3schools.com/sql/sql_groupby.asp)
+- [Pandas GroupBy Documentation](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.groupby.html)
+- [Pandas filter() Documentation](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.filter.html)
+