【讨论中】MySQL5.5的not found是如何被触发的！

ccxpts

在MySQL5.5中触发not found事件的定义为：

DECLARE not_found, i_count INTEGER default 0;
DECLARE c_field1,c_field2,c_field3 char(20);
DECLARE table_csr FOR
    select field1,field2,field3 from my_table;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET not_found=1;

在存贮过程中有三种情况要求触发not_found=1;
1)在循环读取游标至表尾被触发，例：
OPEN table_csr;
table_loop:LOOP
  FETCH table_csr into c_field1,c_field2,c_field3;
  IF not_found=1 THEN
    LEAVE table_loop;
  END IF;
END LOOP table_loop;
CLOSE table_csr;

2)在读取单条记录时时被触发，例
select field1,field2,field3 into c_field1,c_field2,c_field3
from my_table limit 1;
IF not_found=1 THEN
  报错处理;
END IF;
假如my_table返回结果集为空，这种方式在MySQL5.1不会报错，
但在MySQL5.5会报错中断退出，我推测单条SQL查询不会触发NOT FOUND

纠正方法：
select count(*) into i_count from my_table;
IF i_count > 0 THEN
  select field1,field2,field3 into c_field1,c_field2,c_field3
  from my_table limit 1;
END IF;

3)在读取合计金额数时被触发，例
select ifnull(sum(field4), 0) into f_decimal from my_table;
IF not_found=1 THEN
  报错处理
END IF;
在MySQL5.5环境测试中，我发现这种写法不会触发NOT FOUND.

请各位大虾不吝赐正！