Detailed explanation of MySQL's stored procedures, cursors, and transactions

DELIMITER $$
DROP PROCEDURE IF EXISTS `transferEmailTempData`$$

CREATE PROCEDURE transferEmailTempData(IN jobId VARCHAR(24))
BEGIN
  DECLARE idval VARCHAR(24) DEFAULT '';
  DECLARE taskIdval VARCHAR(24) DEFAULT '';
  DECLARE groupIdval VARCHAR(24) DEFAULT '';
  DECLARE emailval VARCHAR(50) DEFAULT '';
  
  /*标识正式表是否存在一条相同数据，即：groupId、email相同*/
  DECLARE infoId VARCHAR(24) DEFAULT '';
  
  /*标识事务错误*/
  DECLARE err INT DEFAULT 0;
  
  /*达到一定数量就进行提交，计数器*/
  DECLARE counts INT DEFAULT 0;
  
  /*标识是否回滚过*/
  DECLARE isrollback INT DEFAULT 0;
  
  /*游标遍历时，作为判断是否遍历完全部记录的标记*/
  DECLARE done INTEGER DEFAULT 0;
  
  /*获取临时表该任务的数据*/
  DECLARE cur CURSOR FOR SELECT id,taskId,groupId,email FROM `t_email_data_temp` WHERE taskId=jobId;
  
  /*根据群组id、email查询是否存在相同记录*/
  DECLARE cur2 CURSOR FOR SELECT id FROM `t_email_info` e WHERE e.`group_id` = groupIdval AND e.`email_address` = emailval; 
  
  /* 出现错误，设置为1，只要发生异常就回滚*/
  DECLARE CONTINUE HANDLER FOR SQLEXCEPTION SET err=1;
  
  /*声明当游标遍历完全部记录后将标志变量置成某个值*/
  DECLARE CONTINUE HANDLER FOR NOT FOUND
  SET done=1;
  
  /*开启事务*/
  START TRANSACTION;
  
  /*打开游标*/
  OPEN cur;
  
  /*使用LOOP循环遍历*/
  out_loop:LOOP
  
    /*将每一条结果对应的字段值赋值给变量*/
    FETCH cur INTO idval,taskIdval,groupIdval,emailval;
    IF done = 1 THEN
      LEAVE out_loop;
    END IF;
    
    /*打开第二个游标*/
    OPEN cur2;
      SET done = 0;
      FETCH cur2 INTO infoId;
      
      /*如果正式表不存在相同groupId and email记录，添加到正式表*/
      IF done = 1 THEN
      
        /*插入正式表*/
        INSERT INTO `t_email_info` VALUES(idval,emailval,groupIdval,0,'',NOW(),'admin',NOW(),'admin');
        
        /*删除临时数据*/
        DELETE FROM `t_email_data_temp` WHERE id = idval;
        
        /*计数器，每1000条才提交*/
        SET counts = counts + 1;
        
        /*发生异常，回滚*/
        IF err=1 THEN
          SET isrollback=1;
          ROLLBACK;
        ELSE
          IF counts = 1000 THEN
            COMMIT;
            /*达到1000条提交后，重置计数器*/
            SET counts=0;
          END IF;
        END IF;
      ELSE
        /*已经存在相同记录，则删除该记录*/
        IF done=0 THEN
          DELETE FROM `t_email_data_temp` WHERE id = idval;
        END IF;
      END IF;
      FETCH cur2 INTO infoId;
    CLOSE cur2;
    
    /*控制外部的循环，该步骤不能缺少，否则只循环一次就结束了*/
    SET done=0;
    
  END LOOP out_loop;
  CLOSE cur;
  
  /*如果没有发生过回滚事件，则更新task状态*/
  /*如果回滚过，不更新task状态，下次执行任务的时候，会再次将剩余没有提交的数据进行添加到正式表*/
  IF isrollback=0 THEN
    UPDATE `t_email_task` t SET t.`if_finish` = 1 WHERE t.`id`=jobId;
  END IF;
  
  END$$

DELIMITER ;