Update readme.md

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LeetCode SQL 50 Solution/1517. Find Users With Valid E-Mails/readme.md

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+Here’s a well-structured `README.md` for **LeetCode 1517 - Find Users With Valid E-Mails**, formatted for a GitHub repository:  
+
+```md
+# 📩 Find Users With Valid E-Mails - LeetCode 1517
+
+## 📌 Problem Statement
+You are given a table **Users** that contains user registration details, including their emails. Some of these emails may be **invalid**.
+
+A valid email:
+- Has a **prefix name** and a **domain**.
+- The prefix:
+  - **Must start with a letter** (uppercase or lowercase).
+  - Can contain **letters**, **digits**, **underscore (`_`)**, **period (`.`)**, and/or **dash (`-`)**.
+- The domain must be **"@leetcode.com"**.
+
+Your task is to **find users with valid emails**.
+
+---
+
+## 📊 Table Structure
+
+### **Users Table**
+| Column Name | Type    |
+| ----------- | ------- |
+| user_id     | int     |
+| name        | varchar |
+| mail        | varchar |
+
+- `user_id` is the **primary key**.
+
+---
+
+## 📊 Example 1:
+
+### **Input:**
+#### **Users Table**
+| user_id | name      | mail                    |
+| ------- | --------- | ----------------------- |
+| 1       | Winston   | winston@leetcode.com    |
+| 2       | Jonathan  | jonathanisgreat         |
+| 3       | Annabelle | bella-@leetcode.com     |
+| 4       | Sally     | sally.come@leetcode.com |
+| 5       | Marwan    | quarz#2020@leetcode.com |
+| 6       | David     | david69@gmail.com       |
+| 7       | Shapiro   | .shapo@leetcode.com     |
+
+### **Output:**
+| user_id | name      | mail                    |
+| ------- | --------- | ----------------------- |
+| 1       | Winston   | winston@leetcode.com    |
+| 3       | Annabelle | bella-@leetcode.com     |
+| 4       | Sally     | sally.come@leetcode.com |
+
+### **Explanation:**
+- ✅ **Valid emails:**
+  - `winston@leetcode.com` ✅ (Starts with a letter, correct domain)
+  - `bella-@leetcode.com` ✅ (Starts with a letter, correct domain)
+  - `sally.come@leetcode.com` ✅ (Starts with a letter, correct domain)
+- ❌ **Invalid emails:**
+  - `jonathanisgreat` ❌ (No domain)
+  - `quarz#2020@leetcode.com` ❌ (Contains `#`, which is not allowed)
+  - `david69@gmail.com` ❌ (Wrong domain)
+  - `.shapo@leetcode.com` ❌ (Starts with a period `.`)
+
+---
+
+## 🖥 SQL Solution
+
+### ✅ **Using `REGEXP_LIKE` (MySQL)**
+#### **Explanation:**
+- Use `REGEXP_LIKE(mail, '^[A-Za-z]+[A-Za-z0-9_.-]*@leetcode\\.com$')`
+  - `^` → Start of string.
+  - `[A-Za-z]+` → First character **must** be a **letter**.
+  - `[A-Za-z0-9_.-]*` → Rest can be **letters, numbers, `_`, `.`, or `-`**.
+  - `@leetcode\\.com$` → Must end with `"@leetcode.com"`.
+
+```sql
+SELECT *
+FROM Users
+WHERE REGEXP_LIKE(mail, '^[A-Za-z]+[A-Za-z0-9_.-]*@leetcode\\.com$');
+```
+
+---
+
+## 📁 File Structure
+```
+📂 Find-Users-With-Valid-Emails
+│── 📜 README.md
+│── 📜 solution.sql
+│── 📜 test_cases.sql
+```
+
+---
+
+## 🔗 Useful Links
+- 📖 [LeetCode Problem](https://leetcode.com/problems/find-users-with-valid-e-mails/)
+- 🔍 [MySQL REGEXP_LIKE Documentation](https://dev.mysql.com/doc/refman/8.0/en/regexp.html)
+- 📝 [SQL Regular Expressions Cheatsheet](https://www.w3schools.com/sql/sql_regex.asp)
+```
+
+### Features of this `README.md`:
+✅ **Clear problem statement with tables**  
+✅ **Example with detailed explanation**  
+✅ **SQL solution breakdown**  
+✅ **File structure for easy organization**  
+✅ **Helpful links for further learning**  
+
+Would you like any modifications? 🚀