QER

Author: iamAntimPal

LeetCode SQL 50 Solution/196. Delete Duplicate Emails/196. Delete Duplicate Emails.sql

@@ -1,3 +1,4 @@
+-- 196. Delete Duplicate Emails
 # Write your MySQL query statement below
 # Write your MySQL query statement below
 DELETE p2 FROM Person p1 

LeetCode SQL 50 Solution/196. Delete Duplicate Emails/readme.md

@@ -0,0 +1,118 @@
+
+# **196. Delete Duplicate Emails**
+
+## **Problem Statement**
+You are given a table called `Person`, which stores email addresses.
+
+### **Person Table**
+```
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| id          | int     |
+| email       | varchar |
++-------------+---------+
+```
+- `id` is the **primary key**.
+- Each row contains an **email address**.
+- All emails are in **lowercase**.
+
+### **Task:**
+Delete all **duplicate emails**, keeping only **one unique email** with the **smallest id**.
+
+---
+
+## **Example 1:**
+### **Input:**
+#### **Person Table**
+```
++----+------------------+
+| id | email            |
++----+------------------+
+| 1  | john@example.com |
+| 2  | bob@example.com  |
+| 3  | john@example.com |
++----+------------------+
+```
+### **Output:**
+```
++----+------------------+
+| id | email            |
++----+------------------+
+| 1  | john@example.com |
+| 2  | bob@example.com  |
++----+------------------+
+```
+### **Explanation:**
+- `john@example.com` appears **twice**.
+- We keep the row with the **smallest `id`** (`id = 1`).
+- The duplicate (`id = 3`) is **deleted**.
+
+---
+
+## **Solution Approaches**
+
+### **SQL Solution (Using Self Join)**
+```sql
+DELETE p2 FROM Person p1 
+JOIN Person p2 
+ON p1.email = p2.email AND p1.id < p2.id;
+```
+**Explanation:**
+- `p1` and `p2` refer to the **same table** (`Person`).
+- We **join** them on `email` to find duplicates.
+- If `p1.id < p2.id`, we delete `p2`, keeping the row with the **smallest id**.
+
+---
+
+### **SQL Solution (Using Subquery)**
+```sql
+DELETE FROM Person
+WHERE id NOT IN (
+    SELECT MIN(id) FROM Person GROUP BY email
+);
+```
+**Explanation:**
+- We **group** by `email` and **select the smallest `id`** for each email.
+- The `DELETE` statement removes rows **not in** this list.
+
+---
+
+### **Pandas Solution**
+```python
+import pandas as pd
+
+def delete_duplicate_emails(person: pd.DataFrame) -> None:
+    # Keep only the first occurrence of each email (smallest id)
+    person.drop_duplicates(subset=['email'], keep='first', inplace=True)
+```
+**Explanation:**
+- `drop_duplicates(subset=['email'], keep='first', inplace=True)`:
+  - Keeps only **the first occurrence** of each email.
+  - Ensures **modification happens in place**.
+
+---
+
+## **File Structure**
+```
+📂 LeetCode196
+│── 📜 problem_statement.md
+│── 📜 sql_self_join_solution.sql
+│── 📜 sql_subquery_solution.sql
+│── 📜 pandas_solution.py
+│── 📜 README.md
+```
+- `problem_statement.md` → Contains the problem description.
+- `sql_self_join_solution.sql` → Contains the SQL solution using **JOIN**.
+- `sql_subquery_solution.sql` → Contains the SQL solution using **Subquery**.
+- `pandas_solution.py` → Contains the Pandas solution for Python users.
+- `README.md` → Provides an overview of the problem and solutions.
+
+---
+
+## **Useful Links**
+- [LeetCode Problem 196](https://leetcode.com/problems/delete-duplicate-emails/)
+- [SQL DELETE Statement](https://www.w3schools.com/sql/sql_delete.asp)
+- [Pandas drop_duplicates()](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.drop_duplicates.html)
+
+---