Question

mysql> describe taps;
+------------+-----------+------+-----+-------------------+-------+
| Field      | Type      | Null | Key | Default           | Extra |
+------------+-----------+------+-----+-------------------+-------+
| tag        | int(11)   | NO   |     | NULL              |       |
| station    | int(11)   | NO   |     | NULL              |       |
| time_Stamp | timestamp | NO   |     | CURRENT_TIMESTAMP |       |
+------------+-----------+------+-----+-------------------+-------+
3 rows in set (0.00 sec)

如何获得每个标记访问过的网站数量，并按最多访问次数排序 - 我们只计算一次访问每个网站，即使有多个访问次数？

随机数据：

mysql> select * from taps;
+-----+---------+---------------------+
| tag | station | time_Stamp          |
+-----+---------+---------------------+
|  50 |      12 | 2016-05-10 20:02:41 |
|  33 |       7 | 2016-05-10 20:02:42 |
|  34 |      13 | 2016-05-10 20:02:42 |
|  31 |       3 | 2016-05-10 20:02:42 |
|   9 |      10 | 2016-05-10 20:02:42 |
|   2 |      11 | 2016-05-10 20:02:42 |
|  33 |      13 | 2016-05-10 20:02:42 |
|  46 |      12 | 2016-05-10 20:02:42 |
|  45 |       1 | 2016-05-10 20:02:42 |
|  34 |       7 | 2016-05-10 20:02:42 |
|   4 |      10 | 2016-05-10 20:08:18 |
|  17 |       5 | 2016-05-10 20:08:19 |
|  46 |       7 | 2016-05-10 20:08:19 |
|  16 |       5 | 2016-05-10 20:08:19 |
|  33 |       3 | 2016-05-10 20:08:19 |
|  31 |       4 | 2016-05-10 20:08:19 |
|   1 |      13 | 2016-05-10 20:08:19 |
|  35 |       2 | 2016-05-10 20:08:19 |
|   9 |      12 | 2016-05-10 20:08:19 |
|  26 |       7 | 2016-05-10 20:08:19 |
+-----+---------+---------------------+
20 rows in set (0.00 sec)

Answer 1

假设我正确理解您的问题，您只需将count与distinct一起使用：

select tag, count(distinct station) cnt
from taps
group by tag
order by 2 desc

Answer 2

使用COUNT功能和GROUP BY查找每个tag的访问次数。

并使用ORDER BY子句按访问次数的降序对结果进行排序。

<强>查询

SELECT tag, COUNT(DISTINCT station) AS `no of visits`
FROM taps
GROUP BY tag
ORDER BY COUNT(DISTINCT station) DESC;

计数和订购

2 个答案: