mysql> select * from a;
+------+----------+
| id   | BIdes    |
+------+----------+
| 1    | 1,3,4,5  |
| 2    | 2,4,8,10 |
+------+----------+
2 rows in set (0.00 sec)

mysql> select * from b;
+------+------+
| id   | name |
+------+------+
| 1    | A    |
| 2    | B    |
| 3    | C    |
| 4    | D    |
| 5    | E    |
+------+------+
5 rows in set (0.00 sec)

mysql> select b.*
    -> from A,b
    -> where a.id=1 And find_in_set(B.id,a.BIdes);
+------+------+
| id   | name |
+------+------+
| 1    | A    |
| 3    | C    |
| 4    | D    |
| 5    | E    |
+------+------+
4 rows in set (0.02 sec)

mysql>

------解决方案--------------------

用你的数据：
select b.* from b left join b on instr(a.BIdes,B.id)>0 where a.id=1