Oracle中游标使用效率比较

鸣谢：http://blog.163.com/gaoyutong122@126/blog/static/344697322012725344964/

扩展：http://www.cnblogs.com/rootq/archive/2008/11/17/1335491.html

批量SQL之 BULK COLLECT 子句：http://blog.youkuaiyun.com/leshami/article/details/7545597

 

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、显式游标
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_ in (select c.cust_name from ea_cust.cust_info c) loop
   
       NULL;  www.2cto.com 
   
    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