Update readme.md

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LeetCode SQL 50 Solution/1045. Customers Who Bought All Products/readme.md

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+Here’s the updated README.md, including **Pandas and Window SQL solutions** along with the original **MySQL solution**.
+
+---
+
+# **1045. Customers Who Bought All Products**
+
+## **Problem Statement**
+You are given two tables:  
+- `Customer` (contains `customer_id` and `product_key`)  
+- `Product` (contains all available `product_key`s)
+
+Each `product_key` in `Customer` is a **foreign key** referring to the `Product` table.
+
+### **Customer Table**
+```
++-------------+-------------+
+| Column Name | Type        |
++-------------+-------------+
+| customer_id | int         |
+| product_key | int         |
++-------------+-------------+
+```
+- The table may contain **duplicate rows**.
+- `customer_id` is **not NULL**.
+- `product_key` refers to the `Product` table.
+
+### **Product Table**
+```
++-------------+
+| product_key |
++-------------+
+| int         |
++-------------+
+```
+- `product_key` is the **primary key** (unique values) of this table.
+
+### **Task:**
+Find **all customer IDs** who bought **every product** listed in the `Product` table.
+
+---
+
+## **Example 1:**
+
+### **Input:**
+**Customer Table**
+```
++-------------+-------------+
+| customer_id | product_key |
++-------------+-------------+
+| 1           | 5           |
+| 2           | 6           |
+| 3           | 5           |
+| 3           | 6           |
+| 1           | 6           |
++-------------+-------------+
+```
+
+**Product Table**
+```
++-------------+
+| product_key |
++-------------+
+| 5           |
+| 6           |
++-------------+
+```
+
+### **Output:**
+```
++-------------+
+| customer_id |
++-------------+
+| 1           |
+| 3           |
++-------------+
+```
+
+### **Explanation:**
+- There are **two products** (5 and 6).
+- Customers who bought **both** products:
+  - **Customer 1**: Bought `5, 6` ✅
+  - **Customer 2**: Bought `6` ❌ (missing `5`)
+  - **Customer 3**: Bought `5, 6` ✅
+- So, **customers 1 and 3** are returned.
+
+---
+
+## **SQL Solutions**
+
+### **1️⃣ Standard MySQL Solution**
+```sql
+SELECT customer_id 
+FROM Customer 
+GROUP BY customer_id
+HAVING COUNT(DISTINCT product_key) = (SELECT COUNT(product_key) FROM Product);
+```
+#### **Explanation:**
+1. **GROUP BY `customer_id`** → Group purchases per customer.
+2. **COUNT(DISTINCT product_key)** → Count unique products each customer bought.
+3. **Compare with total products:**  
+   - `(SELECT COUNT(product_key) FROM Product)` counts all available products.
+   - Only customers with `COUNT(DISTINCT product_key) = total products` are included.
+4. **HAVING** ensures we return only those who bought **all products**.
+
+---
+
+### **2️⃣ Window Function (SQL) Solution**
+```sql
+WITH product_count AS (
+    SELECT COUNT(*) AS total_products FROM Product
+),
+customer_purchase AS (
+    SELECT customer_id, COUNT(DISTINCT product_key) AS purchased_count
+    FROM Customer
+    GROUP BY customer_id
+)
+SELECT customer_id 
+FROM customer_purchase, product_count
+WHERE customer_purchase.purchased_count = product_count.total_products;
+```
+#### **Explanation:**
+1. **CTE `product_count`** → Stores total number of products in `Product` table.
+2. **CTE `customer_purchase`** → Groups purchases per customer and counts distinct products.
+3. **Final SELECT query** → Compares each customer's purchase count with `total_products` and returns only those who match.
+
+---
+
+## **Pandas Solution (Python)**
+```python
+import pandas as pd
+
+# Sample data
+customer_data = {'customer_id': [1, 2, 3, 3, 1],
+                 'product_key': [5, 6, 5, 6, 6]}
+product_data = {'product_key': [5, 6]}
+
+# Create DataFrames
+customer_df = pd.DataFrame(customer_data)
+product_df = pd.DataFrame(product_data)
+
+# Get the total number of products
+total_products = product_df['product_key'].nunique()
+
+# Count distinct products per customer
+customer_purchase = customer_df.groupby('customer_id')['product_key'].nunique()
+
+# Filter customers who bought all products
+result = customer_purchase[customer_purchase == total_products].reset_index()
+
+print(result)
+```
+
+### **Explanation:**
+1. **Create DataFrames** → Convert customer and product tables into Pandas DataFrames.
+2. **Get total unique products** → `product_df['product_key'].nunique()`
+3. **Count distinct products per customer** → `.groupby('customer_id')['product_key'].nunique()`
+4. **Filter customers who match total products** → Customers with `purchased_count == total_products`
+5. **Return final result**.
+
+---
+
+## **File Structure**
+```
+LeetCode1045/
+├── problem_statement.md       # Contains the problem description and constraints.
+├── sql_solution.sql           # Contains the SQL solutions (Standard + Window Functions).
+├── pandas_solution.py         # Contains the Pandas solution.
+├── README.md                  # Overview of the problem and available solutions.
+```
+
+---
+
+## **Useful Links**
+- [LeetCode Problem 1045](https://leetcode.com/problems/customers-who-bought-all-products/)
+- [SQL GROUP BY Documentation](https://www.w3schools.com/sql/sql_groupby.asp)
+- [SQL HAVING Clause](https://www.w3schools.com/sql/sql_having.asp)
+- [Pandas GroupBy Documentation](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.groupby.html)
+
+---ture & Useful Links**  
+
+🚀 **Now it's a complete guide!** 🚀