Added a new question- Find Cumulative Salary of an Employee

Author: Indrajeet Mishra

Find Cumulative Salary of an Employee/README.md

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+# [Find Cumulative Salary of an Employee](https://leetcode.com/problems/find-cumulative-salary-of-an-employee/description/)
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+
+---
+
+## 🛠️ Problem Statement
+
+  <b>Table Name : Employee</b>
+
+|  Column Name  |Type |
+| ------------- | ------------- |
+| id          | int  |
+| month       | int  |
+| salary      | int  |
+
+* (id, month) is the primary key for this table.
+* Each row in the table indicates the salary of an employee in one month during the year 2020.
+<br/>
+
+
+
+Write an SQL query to calculate the cumulative salary summary for every employee in a single unified table.
+</br>
+
+The cumulative salary summary for an employee can be calculated as follows:
+- For each month that the employee worked, sum up the salaries in that month and the previous two months.
+- This is their 3-month sum for that month. If an employee did not work for the company in previous months,
+their effective salary for those months is 0.
+- Do not include the 3-month sum for the most recent month that the employee worked for in the summary.
+- Do not include the 3-month sum for any month the employee did not work.
+
+
+Return the result table ordered by id in ascending order. In case of a tie, order it by month in descending order.
+The query result format is in the following example.
+</br>
+</br>
+ <details>
+<summary>
+Input
+</summary>
+  
+  <b>Table Name: Employee</b>
+
+| id | month | salary |
+| --- |------ |-----|
+| 1  | 1     | 20     |
+| 2  | 1     | 20     |
+| 1  | 2     | 30     |
+| 2  | 2     | 30     |
+| 3  | 2     | 40     |
+| 1  | 3     | 40     |
+| 3  | 3     | 60     |
+| 1  | 4     | 60     |
+| 3  | 4     | 70     |
+| 1  | 7     | 90     |
+| 1  | 8     | 90     |
+
+</details>
+
+<details>
+<summary>
+Output
+</summary>
+
+| id | month | salary |
+| ---- | ---- | ----|
+| 1  | 7     | 90     |
+| 1  | 4     | 130    |
+| 1  | 3     | 90     |
+| 1  | 2     | 50     |
+| 1  | 1     | 20     |
+| 2  | 1     | 20     |
+| 3  | 3     | 100    |
+| 3  | 2     | 40     |
+</details>
+
+---

Find Cumulative Salary of an Employee/schema.sql

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+CREATE TABLE employee (
+    id int,
+    MONTH int,
+    salary int,
+    PRIMARY KEY(id, MONTH)
+);
+
+-- Insert Query:
+INSERT INTO
+    employee (id, MONTH, salary)
+VALUES
+    (1, 1, 20),
+    (2, 1, 20),
+    (1, 2, 30),
+    (2, 2, 30),
+    (3, 2, 40),
+    (1, 3, 40),
+    (3, 3, 60),
+    (1, 4, 60),
+    (3, 4, 70),
+    (1, 7, 90),
+    (1, 8, 90);
+
+COMMIT;

Find Cumulative Salary of an Employee/solution.sql

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+WITH cte AS (
+    SELECT
+        a.id,
+        a.month,
+        b.salary
+    FROM
+        employee a
+        INNER JOIN employee b ON a.id = b.id
+        AND (
+            a.month = b.month
+            OR a.month = b.month + 1
+            OR a.month = b.month + 2
+        )
+),
+cum_sum AS (
+    SELECT
+        id,
+        MONTH,
+        sum(salary) salary
+    FROM
+        cte
+    GROUP BY
+        id,
+        MONTH
+),
+recent_month AS (
+    SELECT
+        id,
+        max(MONTH) recent_month
+    FROM
+        employee
+    GROUP BY
+        id
+)
+SELECT
+    a.id,
+    a.month,
+    a.salary
+FROM
+    cum_sum a
+    INNER JOIN recent_month b ON a.id = b.id
+    AND a.month != b.recent_month
+ORDER BY
+    a.id,
+    a.month DESC;