mysql获取具有最大聚合计数的条目

Question

我有一个 email_patterns 表，我想为每个域找到最常见的模式：

email_patterns
id, domain, pattern
1, microsoft.com, first.last
2, microsoft.com, first.last
3, microsoft.com, last.first
4, microsoft.com, first
5, apple.com, last
6, apple.com, last.first
7, apple.com, last.first

查询应该返回

domain, pattern, count
microsoft.com, first.last, 2
apple.com, last.first, 2

这是获取每个域、模式组合的计数的方法：

SELECT domain, pattern, COUNT(1) count FROM email_patterns GROUP BY domain, pattern;

但是，我只想获取每个域中计数最高的域模式组合。

Answer 1

接下来你只需要ROW_NUMBER():

SELECT domain, pattern, cnt
FROM (SELECT domain, pattern, COUNT(*) as cnt,
             ROW_NUMBER() OVER (PARTITION BY domain ORDER BY COUNT(*) DESC) as seqnum
      FROM email_patterns
      GROUP BY domain, pattern
     ) dp
WHERE seqnum = 1;