删除重复数据

select   *    from  
(
     -- 获取冗余数据中的唯一最小行数据
     select   *    from  table_1 t1
      where  t1.id  in  
    (
         select   min (t2.id)  from  table_1 t2 
         group   by  t2.employeeid  having  t1.employeeid = t2.employeeid  and   count ( * )  >   1
    )
     union   all
     -- 获取非冗余数据
     select   *   from  table_1 t4  where  t4.id  in
    (
         select   min (t3.id)  from  table_1 t3
         group   by  t3.employeeid  having  t4.employeeid  =  t3.employeeid  and   count ( * )  =   1
    )
) t5  order   by  id