mysql> select name, salary from employee
    -> where salary is null or salary < 300000;
+--------------+--------+
| name         | salary |
+--------------+--------+
| 山田太郎     |   NULL |
| 佐藤次郎     | 250000 |
| 鈴木花子     | 250000 |
+--------------+--------+
3 rows in set (0.05 sec)

mysql> select name, birthday from employee
    -> where birthday <= '1990-01-01';
+--------------+------------+
| name         | birthday   |
+--------------+------------+
| 田中三郎     | 1975-11-03 |
| 高橋良子     | 1985-11-23 |
| 鈴木良枝     | 1970-05-03 |
| 佐藤健次     | 1980-05-05 |
+--------------+------------+
4 rows in set (0.01 sec)

mysql> select name, salary from employee
    -> where salary >= 300000 and salary < 400000;
+--------------+--------+
| name         | salary |
+--------------+--------+
| 高橋良子     | 300000 |
| 佐藤健次     | 350000 |
+--------------+--------+
2 rows in set (0.00 sec)

mysql> select name, salary from employee
    -> where salary between 300000 and 399999;
+--------------+--------+
| name         | salary |
+--------------+--------+
| 高橋良子     | 300000 |
| 佐藤健次     | 350000 |
+--------------+--------+
2 rows in set (0.00 sec)

mysql> select name, gender, salary, dep_id from employee
    -> where gender ='男'
    -> or salary >= 400000
    -> or dep_id ='D001';
+--------------+--------+--------+--------+
| name         | gender | salary | dep_id |
+--------------+--------+--------+--------+
| 山田太郎     | 男     |   NULL | NULL   |
| 佐藤次郎     | 男     | 250000 | D001   |
| 田中三郎     | 男     | 400000 | D003   |
| 鈴木良枝     | 女     | 450000 | D003   |
| 佐藤健次     | 男     | 350000 | D001   |
+--------------+--------+--------+--------+
5 rows in set (0.00 sec)