Added Child - Parent - Grandparent Hierarchy

Author: thecoddiwompler

Child - Parent - Grandparent Hierarchy/README.md

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+# Child - Parent - Grandparent Hierarchy
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+
+---
+
+## 🛠️ Problem Statement
+
+
+<b>Table Name : persons</b>
+</br>
+|  Column Name  |Type |
+| ------------- | ------------- |
+| person    | varchar(10) |
+| parent     | varchar(10)    |
+| person_status | varchar(10)     |
+
+
+This table provides Person's Name, their Parent's name, and the Person's Status (If they are Alive or not). 
+<br/>
+</br>
+<b>write an SQL query to return count of people whose grandparent is alive.</b>
+</br>
+</br>
+<b>The query result format is in the following example:  </b>
+</br>
+</br>
+
+ <details>
+<summary>
+Input
+</summary>
+<br>
+<b>Table Name : persons</b>
+<br><br>
+
+| person | parent | person_status |
+|--------|--------|---------------|
+| A      | X      | Alive         |
+| B      | Y      | Dead          |
+| X      | X1     | Alive         |
+| Y      | Y1     | Alive         |
+| X1     | X2     | Alive         |
+| Y1     | Y2     | Dead          |
+
+
+
+
+</details>
+
+<details>
+<summary>
+Output
+</summary>
+<br>
+
+| person_count    | 
+| ---- |
+| 1  |
+</details>
+
+---

Child - Parent - Grandparent Hierarchy/schema.sql

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+CREATE TABLE persons (
+    person varchar(10),
+    parent varchar(10),
+    person_status varchar(10)
+);
+
+INSERT INTO
+    persons (person, parent, person_status)
+VALUES
+    ('A', 'X', 'Alive'),
+    ('B', 'Y', 'Dead'),
+    ('X', 'X1', 'Alive'),
+    ('Y', 'Y1', 'Alive'),
+    ('X1', 'X2', 'Alive'),
+    ('Y1', 'Y2', 'Dead');
+
+COMMIT;

Child - Parent - Grandparent Hierarchy/solution.sql

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+SELECT
+    COUNT(a.person) person_count
+FROM
+    persons a
+    INNER JOIN persons b ON a.parent = b.person
+    INNER JOIN persons c ON b.parent = c.person
+WHERE
+    c.person_status = 'Alive';