重复次数排序的问题
表MB有三个字段A、B、C，数据如下
A                    B                      C
--------------------------------------------
0                          4                          8
1                          4                          8
1                          4                          8
2                          4                          8
2                          4                          8
2                          5                          8
3                          5                          8
3                          5                          8
3                          5                          9
3                          5                          9
3                          5                          9
3                          9