# HackerRank: [SQL Advanced Select] (4/5) BINARY TREE NODES | case, when, if, sub-query in SQL

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SQL Problem Statement:

You are given a table, BST, containing two columns: N and P, where N represents the value of a node in Binary Tree, and P is the parent of N.

Write a query to find the node type of Binary Tree ordered by the value of the node. Output one of the following for each node:

• Root: If node is root node.
• Leaf: If node is leaf node.
• Inner: If node is neither root nor leaf node.

Input Format:

The BST table is described as follows: BST_Columns

Sample Input:
The BST table contains the following records:
Sample Output:
```1 Leaf
2 Inner
3 Leaf
5 Root
6 Leaf
8 Inner
9 Leaf```

Explanation:
The Binary Tree below illustrates the sample:

### Solution-1: Using CASE WHEN Statement (MySQL Query):

```SELECT N,
CASE
WHEN P IS NULL THEN 'Root'
WHEN (SELECT COUNT(*) FROM BST WHERE B.N=P)>0 THEN 'Inner'
ELSE 'Leaf'
END AS PLACE
FROM BST B
ORDER BY N;```

NOTE:
1. Parent for Root Node is Null.
2. Any node which is the parent node of other nodes is an Inner node
3. All remaining nodes are Leaf nodes.

### Solution-2: Using IF Statement (MySQL Query):

```SELECT N,
IF( P IS NULL, 'Root',
IF ((SELECT COUNT(*) FROM BST WHERE B.N = P) > 0, 'Inner', 'Leaf')
) AS PLACE
FROM BST B
ORDER BY N;```

### Sample Output:

```1 Leaf
2 Inner
3 Leaf
4 Inner
5 Leaf
6 Inner
7 Leaf
8 Leaf
9 Inner
10 Leaf
11 Inner
12 Leaf
13 Inner
14 Leaf
15 Root```

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