create or replace procedure copy_data
is
  vn_cnt number(4) := 0;
begin
 select count(*) into vn_cnt from XM_XXK;
 if vn_cnt <> 0 then
   delete from XM_XXK;
 end if;
   insert into XM_XXK as select * from XM_XXX@db_link; --db_link是另外一个数据库的DBLINK;
   commit;
end;

------解决方案--------------------
改一下一楼的.

create or replace procedure copy_data
is
 vn_cnt number(4) := 0;
begin
  select count(*) into vn_cnt from XM_XXK;
  if vn_cnt <> 0 then
  truncate table XM_XXK; --此次避免多次执行后生成高水位线,降低查询速度.
  end if;
  insert into XM_XXK as select * from XM_XXX@db_link; --db_link是另外一个数据库的DBLINK;
  commit;
end;