not nullを入れると、該当のスコアに[0]が表示されます
何か誤りがあるのでしょうか。

drop table if exists users;
create table users (
  id int unsigned,
  name varchar(20),
  score float not null
);

insert into users(id,name,score)values
(1,'taguchi',5.8),
(2,'komiyama',3),
(3,'kurosawa',100),
(4,'akira',null);

↓

mysql> \. ./myapp.sql
Query OK, 0 rows affected (0.01 sec)

Query OK, 0 rows affected (0.03 sec)

Query OK, 4 rows affected, 1 warning (0.01 sec)
Records: 4  Duplicates: 0  Warnings: 1

+------+----------+-------+
| id   | name     | score |
+------+----------+-------+
|    1 | taguchi  |   5.8 |
|    2 | komiyama |     3 |
|    3 | kurosawa |   100 |
|    4 | akira    |     0 |
+------+----------+-------+
4 rows in set (0.00 sec)