求一语句

我想在pubs库中的authors表中作这样一个查询，查出有哪些人的au_lname字段是重复的，也就是说查出最后一个名字是相同的作者以及重复的人数我的语句是这样：select au_lname,number_dups=count(*) from authors group by au_lname
但得到的结果是au_lname                                 number_dups 
---------------------------------------- ----------- 
Bennet                                   1
Blotchet-Halls                           1
Carson                                   1
DeFrance                                 1
del Castillo                             1
Dull                                     1
Green                                    1
Greene                                   1
Gringlesby                               1
Hunter                                   1
Karsen                                   1
Locksley                                 1
MacFeather                               1
McBadden                                 1
O'Leary                                  1
Panteley                                 1
Ringer                                   2
Smith                                    1
Straight                                 1
Stringer                                 1
White                                    1
Yokomoto                                 1（所影响的行数为 22 行）
我想把重复的提出来，其他的不要，只要
au_lname                                 number_dups 
---------------------------------------- ----------- 
Ringer                                   2不知该怎样做，请高手指点