Question 13: Given the following scenario, what is the result of the query below?

mysql> create table dfttst (a int null default null,
b int null default 0,c int not null default 0);
Query OK, 0 rows affected (0.07 sec)

mysql> insert into dfttst values (1,1,1),(null,null,null),(0,0,0);
Query OK, 3 rows affected, 1 warning (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 1

mysql> show warnings;
+---------+------+---------------------------+
| Level   | Code | Message                   |
+---------+------+---------------------------+
| Warning | 1048 | Column 'c' cannot be null |
+---------+------+---------------------------+
1 row in set (0.05 sec)

 
What is the result of the query below?

select count(a),count(b),count(c) from dfttst;

a) 2,2,2
b) 3,3,3
c) 2,2,3

 
And still an extra question:
What would “select a + b + c from tt.dfttst;” return?
 
[ Data Types (15%) - Handling Missing or Invalid Data Values ]