Mentors With At Least Five Mentees

Problem

Table: `Researcher`

```text
+-------------+---------+
| Column | Type |
+-------------+---------+
| res_id | int |
| full_name | varchar |
| lab | varchar |
| mentor_id | int |
+-------------+---------+
res_id is the primary key. mentor_id is the res_id of this researcher's mentor, or NULL if they have no mentor. Nobody mentors themselves.
```

Find every researcher who is the direct mentor of **at least five** other researchers. Return their `full_name` in any order.

**Example**

```text
Researcher:
+--------+---------+-----+-----------+
| res_id | full_name | lab | mentor_id |
+--------+---------+-----+-----------+
| 1 | Noa | X | NULL |
| 2 | Eli | X | 1 |
| 3 | Tal | X | 1 |
| 4 | Roi | X | 1 |
| 5 | Mia | X | 1 |
| 6 | Ari | Y | 1 |
+--------+---------+-----+-----------+

Output:
+-----------+
| full_name |
+-----------+
| Noa |
+-----------+
```

Noa mentors five researchers (Eli, Tal, Roi, Mia, Ari), so she qualifies.

Tables

Example rows — the live problem includes the full dataset.

Expected output

Your answer should return 1 row with the columns full_name.

Starter code (SQL)

SELECT *
FROM Researcher;

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