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 (0.00 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)