没有更多的数据要从套接字读取

我的程序是这样的:

Declare 
       cur_1        Sys_Refcursor;
       cur_2        Sys_Refcursor;
       v_1          VARCHAR2(30);
       v_2          VARCHAR2(30);
       v_3          VARCHAR2(30);
       v_4          VARCHAR2(30);
Begin
       OPEN cur_1 for Select * from tab1@dblink1;
       Loop
           Fetch cur_1 into v_1, v_2;
           EXIT WHEN cur_1%NOTFOUND;   
           OPEN cur_2 for Select * from tab2@dblink1 where col1 = v_1 and col2 = v2;
           Loop
               Fetch cur2 into v_3, v_4;
               Exit when cur_2%notfound;    
               INSERT INTO local.tab3 values (v_1,v_2, v_3, v_4);
           END Loop;
           close cur_2;
       End Loop;
       close cur_1; 
END;

abobe 程序可以编译，但是当我运行它时出现以下错误:

insert into local.tab3(col1, col2, col3, col4)
select tab1.col1, tab1.col2, tab2.col1, tab2.col2
from tab1@dblink1 tab1
join tab2@dblink1 tab2
    on tab1.col1 = tab2.col1
    and tab1.col2 = tab2.col2;