mysql - 我怎样才能计算帖子的数量？

Question

这是我的表结构:

-- reputations
+----+-------------+---------+-------+------------+------------+
| id | post_id     | user_id | score | reputation | date_time  |
+----+-------------+---------+-------+------------+------------+ -- Suppose:
| 1  | 1           | 1       | 1     | 5          | 1500489844 | -- out of last week
| 2  | 4           | 3       | -1    | -2         | 1500499815 | -- out of last week
| 3  | 2           | 3       | 1     | 5          | 1500584821 |
| 4  | 3           | 1       | 1     | 5          | 1501389166 |
| 5  | 2           | 4       | 1     | 5          | 1501399142 |
| 6  | 2           | 1       | -1    | -2         | 1501399142 |
| 7  | 4           | 1       | 0     | 15         | 1501481186 |
| 8  | 5           | 1       | 1     | 5          | 1501481297 |
+----+-------------+---------+-------+------------+------------+
-- Note: the last row came from an accepted-answer, that's why its score is 0

-- post_tag
+---------+--------+
| post_id | tag_id |
+---------+--------+
| 1       | 2      |
| 1       | 4      |
| 2       | 2      |
| 3       | 1      |
| 3       | 4      |
| 4       | 3      |
| 5       | 1      |
+---------+--------+

-- tags
+----+--------+
| id |  name  |
+----+--------+
| 1  | php    |
| 2  | html   |
| 3  | css    |
| 4  | mysql  |
+----+--------+

这是我的查询:

SELECT
    t.tag, sum(r.reputation) AS tag_reputation, sum(r.score) AS tag_score
FROM
    users u
    LEFT JOIN reputations r 
        ON r.user_id = u.id 
            AND r.date_time > 1500584821
    JOIN post_tag pt ON pt.post_id = r.post_id
    JOIN tags t ON t.id = pt.tag_id
WHERE u.id = 1 -- Specific user: Jack
GROUP BY
    u.id, u.user_name, t.tag 
ORDER BY
    u.id, tag_reputation DESC;

这是当前的结果:

tag   | tag_reputation |  tag_score
----: | :------------- | :---------
css   |             15 |          0
php   |             10 |          2
mysql |              5 |          1
html  |             -2 |         -1

如您所见，结果是一个标签列表，其中包含按 tag_reputation 排序的特定用户的声誉和分数。 <强> Fiddle

---

现在我还想计算每个标签的帖子数。所以这是预期的结果:

tag   | tag_reputation |  tag_score | post_num
----: | :------------- | :--------- | :-------
css   |             15 |          0 |        1
php   |             10 |          2 |        2
mysql |              5 |          1 |        1
html  |             -2 |         -1 |        1

我该怎么做？我想我必须处理 post_id 列和 GROUP BY 子句。但我不知 Prop 体如何。

Answer 1

您是否尝试将帖子 ID 添加到查询中？

我在您的select 语句中添加了count(r.post_id) as post_num 并且它gave the expected results .

要删除重复项，请使用 distinct。你想要关于标签表的计数吗？尝试

1. COUNT(distinct pt.post_id) AS post_count;或
2. COUNT(distinct r.post_id) AS post_count