sql中like与%%的用法

mysql> select * from a;
+-------+----------+
| id    | name     |
+-------+----------+
| 1000  | zhangsan |
| 2000  | lisi     |
| 3000  | NULL     |
+-------+----------+
3 rows in set

mysql>

mysql> select * from a
-> where name like '%%';
+-------+----------+
| id    | name     |
+-------+----------+
| 1000  | zhangsan |
| 2000  | lisi     |
+-------+----------+
2 rows in set

mysql>

mysql> select * from b;
+-------+--------+
| id    | goods  |
+-------+--------+
| 1000  | TV     |
| 2000  | Camera |
| 3000  | cup    |
| 4000  | box    |
+-------+--------+
4 rows in set

mysql> select * from b
-> where goods like '%%';
+-------+--------+
| id    | goods  |
+-------+--------+
| 1000  | TV     |
| 2000  | Camera |
| 3000  | cup    |
| 4000  | box    |
+-------+--------+
4 rows in set

mysql>