mysql in和not in

mysql> select * from table1;
+----------+------------+-----+---------------------+-------+
| name_new | transactor | pid | order_date          | price |
+----------+------------+-----+---------------------+-------+
| 1hahha   | 1xiaohong  |    | -- :: |      |
| 2hahha   | 2xiaohong  |    | -- :: |      |
| 3hahha   | 3xiaohong  |    | -- :: |      |
| 4hahha   | 4xiaohong  |    | -- :: |      |
| 3hahha   | bob        |    | -- :: |      |
| 3hahha   | lee        |    | -- :: |      |
| 3hahha   | lee        |    | -- :: |      |
| 3hahha   | lee        |    | -- :: |      |
| 3hahha   | bob        |    | -- :: |      |
| 3hahha   | bob        |   | -- :: |      |
+----------+------------+-----+---------------------+-------+
 rows in set (0.00 sec)

mysql> select * from table1 where pid in (,);
+----------+------------+-----+---------------------+-------+
| name_new | transactor | pid | order_date          | price |
+----------+------------+-----+---------------------+-------+
| 2hahha   | 2xiaohong  |    | -- :: |      |
| 3hahha   | bob        |    | -- :: |      |
+----------+------------+-----+---------------------+-------+
 rows in set (0.01 sec)

mysql> select * from table1 where pid not in (,);
+----------+------------+-----+---------------------+-------+
| name_new | transactor | pid | order_date          | price |
+----------+------------+-----+---------------------+-------+
| 1hahha   | 1xiaohong  |    | -- :: |      |
| 3hahha   | 3xiaohong  |    | -- :: |      |
| 4hahha   | 4xiaohong  |    | -- :: |      |
| 3hahha   | lee        |    | -- :: |      |
| 3hahha   | lee        |    | -- :: |      |
| 3hahha   | lee        |    | -- :: |      |
| 3hahha   | bob        |    | -- :: |      |
| 3hahha   | bob        |   | -- :: |      |
+----------+------------+-----+---------------------+-------+
 rows in set (0.00 sec)