Question

我在MySQL中有这个程序（不用弄清楚它的功能，只需看看光标打开的部分）

/* PROCEDURE 1 : Post notification */
DROP PROCEDURE IF EXISTS AddNotificationOnPosts;

DELIMITER $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `AddNotificationOnPosts`(arg_from_user INT(11),arg_on_post_id INT(11),arg_in_group_id INT(11))
BEGIN
    DECLARE num_rows INT DEFAULT NULL;
    DECLARE insert_result INT DEFAULT NULL;

    DECLARE done INT DEFAULT 0;
    DECLARE var_user_id INT DEFAULT NULL;
        DECLARE c1 CURSOR FOR 
        SELECT user_id 
        FROM user_rights 
        WHERE user_rights.right = 101 AND user_rights.group_id  = arg_in_group_id 
        ORDER BY user_id DESC;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

    IF(arg_from_user IS NULL OR arg_from_user = '')
    THEN
        SELECT "0" AS response;
    ELSEIF(arg_on_post_id IS NULL OR arg_on_post_id = '')
    THEN
        SELECT "0" AS response;
    ELSEIF(arg_in_group_id IS NULL OR arg_in_group_id = '')
    THEN
        SELECT "0" AS response;
    ELSE
        SELECT count(notification_id) FROM notifications_posts 
        WHERE 
        from_user = arg_from_user AND
        on_post_id = arg_on_post_id AND
        in_group_id = arg_in_group_id
        INTO num_rows;
    END IF;

    IF num_rows = 0
    THEN
        INSERT INTO notifications_posts(from_user,on_post_id,in_group_id) VALUES(arg_from_user,arg_on_post_id,arg_in_group_id);
        SELECT ROW_COUNT() INTO insert_result;

        IF insert_result > 0 
        THEN        
            /* Increment the notifications for every user*/
            OPEN c1;
            read_loop: LOOP
                FETCH c1 INTO var_user_id;
                    IF done THEN
                        LEAVE read_loop;
                    ELSE
                        IF NOT(var_user_id = arg_from_user)
                        THEN

                            /* UPDATING */
                            UPDATE user_info SET notifications = notifications + 1 WHERE user_info.user_id = var_user_id;

                            /* SELECTING RESULT */
                            SELECT
                            user_info.user_id,
                            messages,
                            tasks,
                            notifications,
                            messages+tasks+notifications AS total
                            FROM user_rights
                            INNER
                                JOIN user_info
                                ON user_info.user_id = user_rights.user_id
                            WHERE user_rights.right = 101 AND user_rights.group_id  = arg_in_group_id ;

                        END IF;
                    END IF;
            END LOOP;
            CLOSE c1;


        ELSE
            SELECT "0" AS response;
        END IF;

    ELSE
        SELECT "0" AS response;
    END IF;
END $$
DELIMITER ;

并在此部分

            /* Increment the notifications for every user*/
            OPEN c1;
            read_loop: LOOP
                FETCH c1 INTO var_user_id;
                    IF done THEN
                        LEAVE read_loop;
                    ELSE
                        IF NOT(var_user_id = arg_from_user)
                        THEN

                            /* UPDATING */
                            UPDATE user_info SET notifications = notifications + 1 WHERE user_info.user_id = var_user_id;

                            /* SELECTING RESULT */
                            SELECT
                            user_info.user_id,
                            messages,
                            tasks,
                            notifications,
                            messages+tasks+notifications AS total
                            FROM user_rights
                            INNER
                                JOIN user_info
                                ON user_info.user_id = user_rights.user_id
                            WHERE user_rights.right = 101 AND user_rights.group_id  = arg_in_group_id ;

                        END IF;
                    END IF;
            END LOOP;
            CLOSE c1;

程序选择数据，然后更新它（相信我，我已经死了），我真的需要选择之后，因为我生成了XML的数据，这样：

1为什么选择然后更新，因为我看到select位于更新

下面

2谁有这个＆＃34;出色的想法＆＃34;这样做？

谢谢。

Answer 1

当您在sql-server中进行一次批量更新/删除和其他操作时，完全不确定将执行“命令”的顺序。这个问题的解决方案是使用“exec”语句将“update”放在不同的批处理中。所以尝试使用：

exec('UPDATE user_info SET notifications = notifications + 1 WHERE user_info.user_id =' + var_user_id);

现在应该可以了。

Answer 2

我解决了问题：SELECT语句必须在CURSOR LOOP之外。

Answer 3

我认为更新和选择是按照正确的顺序执行的，但是选择不能＆＃34;参见＆＃34;由于事务隔离而导致的更新结果。

我建议使用以下解决方案来解决此问题并通过消除后续选择中的连接来提高性能：

set @notification = 0;

/* UPDATING */
UPDATE user_info SET notifications = @notification := notifications + 1 WHERE user_info.user_id = var_user_id;

/* SELECTING RESULT */
SELECT
     user_info.user_id,
     messages,
     tasks,
     notifications,
     messages+tasks+@notifications AS total
 FROM user_rights
WHERE user_rights.right = 101 AND user_rights.group_id  = arg_in_group_id ;

强制首先更新然后在过程中选择

3 个答案: