对300万一张表数据，用游标进行循环，不同写法的效率比较
1、显示游标
declare
cursor cur_2 is select a.cust_name from ea_cust.cust_info a;
cust_id varchar2(100);
begin
open cur_2;
loop
fetch cur_2 into cust_id;
exit when cur_2%notfound;
NULL;
end loop;
close cur_2;
end;
--耗时48秒
2、隐式游标
declare
begin
for cur_2 in (select c.cust_name from ea_cust.cust_info c) loop
NULL;
end loop;
end;
--耗时16秒
3、bulk collect into + cursor
declare
cursor cur_3 is select a.cust_name from ea_cust.cust_info a;
type t_table is table of varchar2(100);
c_table t_table;
to_cust_id varchar2(100);
begin
open cur_3;
loop
fetch cur_3 bulk collect into c_table limit 100;
exit when c_table.count = 0;
for i in c_table.first..c_table.last loop
null;
end loop;
end loop;
commit;
end;
--耗时13秒，看样子这种最快
