Which of the queries will return 3 sql records?

Question

SQL

Given table nums with data:
id | num
---+----
1 | 1
2 | null
3 | 2
2 | null
3 | 5
3 | 7
Which of the following queries will return exactly 3 records from this table:
1. SELECT 3 FROM nums;
2. SELECT id FROM nums;
3. SELECT num FROM nums WHERE num IS NOT NULL;
4. SELECT DISTINCT id FROM nums;
5. SELECT COUNT(DISTINCT id) FROM nums;
6. SELECT * FROM nums WHERE id <> num;
7. SELECT DISTINCT id FROM nums WHERE num IS NOT NULL;

Answer 1

4. SELECT DISTINCT id FROM nums;
--------------
id
1
2
3
6. SELECT * FROM nums WHERE id <> num;
id | num
------------
3 | 2
3 | 5
3 | 7