Very Simple SQL question ... hepl ? ...

I have a table called names that has last_name and pid in   the table. I am tryint to find a simple query that   will all me to select all rows that have duplicated last names.

   For example

        last_name       pid
       --------------------------
         smith           1
         smith           3
         jones           4
         griffin         5
         stevens         6
         stevens         7

     I want to do the opposite of distinct.
  
     something like ....
       select duplicate last_name pid from person.

         smith           1
         smith           3
         stevens         6
         stevens         7

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