Mysql 存储过程，开启游标循环后，重复循环插入多次数据。

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本文链接： https://blog.csdn.net/wangliuqi123/article/details/84342560

今天在写存储过程，给其他表插入数据时，发现，我游标取出来的数据明明只有一条，但是在循环过程中，却发现插入了两条数据。下面是代码

BEGIN
	#Routine body goes here...
	DECLARE event_content1 VARCHAR(255);
	DECLARE event_id1 INT;
	DECLARE event_name VARCHAR(255);
	DECLARE start_time1 TIMESTAMP;
	DECLARE end_time1 TIMESTAMP;
	DECLARE  result_counts1 INT;
	DECLARE High_result_time1 TIMESTAMP;
	DECLARE high_result_counts1 INT;
	DECLARE start_result_time1 TIMESTAMP;
	DECLARE start_result_name1 text;
	DECLARE reposts_counts1 INT;
	DECLARE comments_counts1 INT;
	DECLARE attitude_counts1 INT;
DECLARE done INT DEFAULT FALSE;
	DECLARE  cur cursor for SELECT id,event_content,create_time,finish_time FROM t_public_concern_event WHERE `status` = 1  ;
	DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
	OPEN cur;
	TRUNCATE TABLE event_preview;
	read_loop:LOOP
    
		if done THEN
            LEAVE read_loop;
            END IF;
		# 游标 获取事件列表
		FETCH cur INTO event_id1,event_content1,start_time1,end_time1;
		# 获取事件相关结果数
		select COUNT(1) INTO result_counts1 from t_public_opinion_realtime_weibo WHERE title= event_content1;
		# 获取事件最多的某一天,以及总数
		SELECT counts,create_time into high_result_counts1,High_result_time1  FROM (select COUNT(1) as counts,DATE_FORMAT(create_time,"%Y-%m-%d") as create_time FROM t_public_opinion_realtime_weibo WHERE title=event_content1 GROUP BY DATE_FORMAT(create_time,"%Y-%m-%d")) as a WHERE a.counts = (SELECT MAX(counts) from (select COUNT(1) as counts,DATE_FORMAT(create_time,"%Y-%m-%d") FROM t_public_opinion_realtime_weibo WHERE title=event_content1 GROUP BY DATE_FORMAT(create_time,"%Y-%m-%d")) as b);
		# 获取事件源头
		SELECT text,create_time into start_result_name1,start_result_time1 from t_public_opinion_realtime_weibo WHERE title = event_content1 ORDER BY create_time LIMIT 1;
		# 总转发 总点赞，总评论
		select SUM(reposts_count) ,SUM(comments_count) , SUM(attitudes_count) INTO reposts_counts1,comments_counts1,attitude_counts1  from t_public_opinion_realtime_weibo WHERE title = event_content1;   
		INSERT INTO event_preview (event_id,start_time,end_time,result_counts,High_result_time,high_result_counts,start_result_time,start_result_name,reposts_counts,comments_counts,attitude_counts)VALUES(event_id1,start_time1,end_time1,result_counts1,High_result_time1,high_result_counts1,start_result_time1,start_result_name1,reposts_counts1,comments_counts1,attitude_counts1);
	END LOOP;
CLOSE cur;
END

结果造成了游标取出来是一条，但是插入却出现两条：

检查后发现没有错， 后来修改，查找，发现是Fetch  游标的位置不对，造成的。

正确的写法是在判断游标为空 也就是 IF 之前 fetch 游标：

OPEN cur;
	TRUNCATE TABLE event_preview;
	read_loop:LOOP
    # 在if 之前fetch 游标
    FETCH cur INTO event_id1,event_content1,start_time1,end_time1;
		if done THEN
            LEAVE read_loop;
            END IF;
		# 其他操作
        。。。。。。。

这样下来就没错了。