MySQL游标循环取出空值的BUG

DELIMITER //
DROP PROCEDURE IF EXISTS Del_Dup_FOR_TEST;
CREATE PROCEDURE Del_Dup_FOR_TEST()
BEGIN
DECLARE min_id INT;
DECLARE v_start_time,v_end_time DATETIME;
DECLARE v_count INT;
DECLARE done INT DEFAULT 0;
DECLARE my_cur CURSOR FOR SELECT start_time,end_time,min(id),count(1) AS count FROM leo.test GROUP BY start_time,end_time HAVING count>1;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
OPEN my_cur;
　　myloop: LOOP
　　FETCH my_cur INTO v_start_time,v_end_time,min_id,v_count;
　　IF done=1 THEN
　　LEAVE myloop;
　　END IF;
　　DELETE FROM leo.test WHERE start_time=v_start_time AND end_time=v_end_time AND id>min_id;
　　COMMIT;
　　END LOOP myloop;
CLOSE my_cur;
END;
//
DELIMITER ;

DELIMITER //
DROP PROCEDURE IF EXISTS Del_Dup_FOR_TEST;
CREATE PROCEDURE Del_Dup_FOR_TEST()
BEGIN
DECLARE min_id INT;
DECLARE start_time,end_time DATETIME;
DECLARE count INT;
DECLARE done INT DEFAULT 0;
DECLARE my_cur CURSOR FOR SELECT start_time,end_time,min(id),count(1) AS count FROM leo.test GROUP BY start_time,end_time HAVING count>1;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
OPEN my_cur;
　　myloop: LOOP
　　FETCH my_cur INTO start_time,end_time,min_id,count;
　　IF done=1 THEN
　　LEAVE myloop;
　　END IF;
　　DELETE FROM leo.test WHERE start_time=start_time AND end_time=end_time AND id>min_id;
　　COMMIT;
　　END LOOP myloop;
CLOSE my_cur;
END;
//
DELIMITER ;

Posted by Brent Roady on May 9, 2012
It should be noted that the local variable names used in FETCH [cursor] INTO must be different than the variable names used in the SELECT statement 
defining the CURSOR. Otherwise the values will be NULL. 
In this example, 
DECLARE a VARCHAR(255);
DECLARE cur1 CURSOR FOR SELECT a FROM table1;
FETCH cur1 INTO a;
the value of a after the FETCH will be NULL.
This is also described here: http://bugs.mysql.com/bug.php?id=28227

Posted by Jérémi Lassausaie on February 3, 2015
Answer for Brent Roady :
I don't see any bug in the bahaviour described.
DECLARE a VARCHAR(255);
/* you declare a variable "a" without a specified default value, a=NULL */
DECLARE cur1 CURSOR FOR 
SELECT a FROM table1;
/* You declare a cursor that selects "a" FROM a table */
OPEN cur1;
/* You execute your cursor query, a warning is raised because a is ambiguously defined but you don't see it */
FETCH cur1 INTO a;
/* you put your unique field in your unique row into a (basically you do "SET a=a;") so a is still NULL */
There is no bug report, just a misunderstanding.