mysql - 如何获取具有重复列的行数？

Question

假设下面是我的表格

id | name | topic | reply
...
1 | user1 | 00001 | yes              ## replied on topic 00001
2 | user2 | 00002 | yes              ** replied on topic 00002
3 | user1 | 00001 | yes              ## replied on topic 00001
4 | user5 | 00001 | no
5 | user1 | 00001 | yes              ## replied on topic 00001
6 | user1 | 00002 | no
7 | user2 | 00002 | yes              ** replied on topic 00002
8 | user3 | 00001 | no
9 | user4 | 00002 | yes

假设这是一个主题表。只有 user1 和 user 对单个主题回复不止一次(主题 00001 和 00002) 如何选择多次回复某个主题的用户数量，应该从 5 返回 2

Answer 1

这将为您提供针对某个主题多次回复的用户数量:

SELECT COUNT(DISTINCT name)
FROM (
    SELECT name
    FROM  yourtable
    WHERE reply = 'yes'
    GROUP BY name, topic
    HAVING COUNT(*) > 1
) T1