选择按id排序的唯一行

I have two tables

我有两个表

Table A

表一个

+-----+---------+---------+
| pid | name    | country |
+-----+---------+---------+
|  1  | ABC     | XXXXXXX |
|  2  | EFG     | YYYYYYY |
|  3  | IJK     | ZZZZZZZ |
|  4  | LMN     | AAAAAAA |
|  5  | OPQ     | BBBBBBB |
|  6  | RST     | CCCCCCC |
+-----+---------+---------+
+--