如何在我的数据库中实现Twitter转发操作

Question

我正在实现类似于Twitter的Web应用程序.我需要实施"转发"动作,一条推文可以多次转发一个人.

我有一个基本的'推文'表,其中包含以下列:

推文: tweet_id | tweet_text | tweet_date_created | tweet_user_id

(tweet_id推文的主键,tweet_text包含推文文本,tweet_date_created是创建推文时的DateTime,tweet_user_id是users表的外键,表示创建推文的用户)

现在我想知道如何在我的数据库中实现转推动作.

选项1

我应该创建新的连接表,如下所示:

锐推:tweet_id | user_id | retweet_date_retweeted

(表tweet_id的外键在哪里,是tweets表user_id的外键,users并标识转发了推文的用户,retweet_date_retweeted是指定转发何时完成的DateTime.)

优点:没有空列,当用户进行reteet时,retweets将创建表中的新行.

缺点:查询过程将更加困难,它需要连接两个表,并以某种方式按两个日期排序推文(当推文不转发时,通过tweet_date_created对其进行排序,当推文转推时,通过retweet_date_retweeted对其进行排序).

选项2

或者我应该在tweets表中实现它parent_id,它将如下所示:

推文: tweet_id | tweet_text | tweet_date_created | tweet_user_id | PARENT_ID

(其中所有列保持不变并且parent_id是同一个tweets表的外键.当创建推文时,parent_id保持为空.当转发推文时,parent_id包含原始推文id,tweet_user_id包含处理转推动作的用户,tweet_date_created包含转发时的DateTime完成,并tweet_text保持空白 - 因为我们不会让用户在转发时更改原始推文.)

专业人士:查询过程更加优雅,因为我不必加入两个表.

缺点:每次转发推文都会有空单元格.因此,如果我的数据库中有1 000条推文,并且每个推文都被转发5次,那么我的tweets表格中将有5 000条线路.

---

哪种方式最有效？拥有空单元格或查询过程更干净更好吗？

Answer 1

IMO选项#1会更好.加入tweet和转推表的查询并不复杂,可以通过左连接或内连接来完成,具体取决于您是要显示所有推文还是仅显示转发的推文.并且连接查询应该是高性能的,因为表是窄的,被连接的列是整数,并且由于FK约束它们将各自具有索引.

另一个建议是不要用tweet或转发标记所有列,这些可以从存储数据的表中推断出来,例如:

tweet
    id
    user_id
    text
    created_at

retweet
    tweet_id
    user_id
    created_at

和样本连接:

# Return all tweets which have been retweeted
SELECT
    count(*),
    t.id
FROM
    tweet AS t
INNER JOIN retweet AS rt ON rt.tweet_id = t.id
GROUP BY
    t.id

# Return tweet and possible retweet data for a specific tweet
SELECT
    t.id
FROM
    tweet AS t
LEFT OUTER JOIN retweet AS rt ON rt.tweet_id = t.id
WHERE
    t.id = :tweetId

- 按要求更新 -

以下只是说明,代表为什么我会选择选项#1,没有外键也没有任何索引,你必须自己添加.但结果应该证明连接不会太痛苦.

CREATE TABLE `tweet` (
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
    `user_id` int(10) unsigned NOT NULL,
    `value` varchar(255) NOT NULL,
    `created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=8 DEFAULT CHARSET=utf8

CREATE TABLE `retweet` (
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
    `tweet_id` int(10) unsigned NOT NULL,
    `user_id` int(10) unsigned NOT NULL,
    `created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

# Sample Rows

mysql> select * from tweet;
+----+---------+----------------+---------------------+
| id | user_id | value          | created_at          |
+----+---------+----------------+---------------------+
|  1 |       1 | User1 | Tweet1 | 2012-07-27 00:04:30 |
|  2 |       1 | User1 | Tweet2 | 2012-07-27 00:04:35 |
|  3 |       2 | User2 | Tweet1 | 2012-07-27 00:04:47 |
|  4 |       3 | User3 | Tweet1 | 2012-07-27 00:04:58 |
|  5 |       1 | User1 | Tweet3 | 2012-07-27 00:06:47 |
|  6 |       1 | User1 | Tweet4 | 2012-07-27 00:06:50 |
|  7 |       1 | User1 | Tweet5 | 2012-07-27 00:06:54 |
+----+---------+----------------+---------------------+

mysql> select * from retweet;
+----+----------+---------+---------------------+
| id | tweet_id | user_id | created_at          |
+----+----------+---------+---------------------+
|  1 |        4 |       1 | 2012-07-27 00:06:37 |
|  2 |        3 |       1 | 2012-07-27 00:07:11 |
+----+----------+---------+---------------------+

# Query to pull all tweets for user_id = 1, including retweets and order from newest to oldest

select * from (
    select t.* from tweet as t where user_id = 1
    union
    select t.* from tweet as t where t.id in (select tweet_id from retweet where user_id = 1))
a order by created_at desc;

mysql> select * from (select t.* from tweet as t where user_id = 1 union select t.* from tweet as t where t.id in (select tweet_id from retweet where user_id = 1)) a order by created_at desc;
+----+---------+----------------+---------------------+
| id | user_id | value          | created_at          |
+----+---------+----------------+---------------------+
|  7 |       1 | User1 | Tweet5 | 2012-07-27 00:06:54 |
|  6 |       1 | User1 | Tweet4 | 2012-07-27 00:06:50 |
|  5 |       1 | User1 | Tweet3 | 2012-07-27 00:06:47 |
|  4 |       3 | User3 | Tweet1 | 2012-07-27 00:04:58 |
|  3 |       2 | User2 | Tweet1 | 2012-07-27 00:04:47 |
|  2 |       1 | User1 | Tweet2 | 2012-07-27 00:04:35 |
|  1 |       1 | User1 | Tweet1 | 2012-07-27 00:04:30 |
+----+---------+----------------+---------------------+

请注意,在最后一组结果中,我们还能够包含转发并在转发#3之前显示转发#4.

- 更新 -

您可以通过稍微更改查询来完成您要求的任务:

select * from (
    select t.id, t.value, t.created_at from tweet as t where user_id = 1
    union
    select t.id, t.value, rt.created_at from tweet as t inner join retweet as rt on rt.tweet_id = t.id where rt.user_id = 1)
a order by created_at desc;

mysql> select * from (select t.id, t.value, t.created_at from tweet as t where user_id = 1 union select t.id, t.value, rt.created_at from tweet as t inner join retweet as rt on rt.tweet_id = t.id where rt.user_id = 1) a order by created_at desc;
+----+----------------+---------------------+
| id | value          | created_at          |
+----+----------------+---------------------+
|  3 | User2 | Tweet1 | 2012-07-27 00:07:11 |
|  7 | User1 | Tweet5 | 2012-07-27 00:06:54 |
|  6 | User1 | Tweet4 | 2012-07-27 00:06:50 |
|  5 | User1 | Tweet3 | 2012-07-27 00:06:47 |
|  4 | User3 | Tweet1 | 2012-07-27 00:06:37 |
|  2 | User1 | Tweet2 | 2012-07-27 00:04:35 |
|  1 | User1 | Tweet1 | 2012-07-27 00:04:30 |
+----+----------------+---------------------+