计算两个客户之间的最高会话数

Question

我有一个名为电子邮件的表,其中三列表示id,emailFrom,emailTo

--------------------------------------------------
| id | emailFrom        | EmailT0                |
--------------------------------------------------
| 1  | A                | B                      |
--------------------------------------------------
| 2  | B                | A                      |
--------------------------------------------------
| 3  | A                | B                      |
--------------------------------------------------
| 4  | C                | A                      |
--------------------------------------------------
| 5  | B                | C                      |
--------------------------------------------------
| 6  | A                | C                      |
--------------------------------------------------
| 7  | A                | B                      |
--------------------------------------------------

现在我的问题是,如何找出两个客户之间的最高对话

即发送邮件给B和B发送邮件给A,这意味着他们有计数2的对话.现在,
我想找到哪些用户发送了大多数电子邮件给对方

Answer 1

这将返回已发送大多数电子邮件的用户:

SELECT
  LEAST(emailFrom, emailTo) email1,
  GREATEST(emailFrom, emailTo) email2,
  COUNT(*)
FROM
  yourtable
GROUP BY
  LEAST(emailFrom, emailTo),
  GREATEST(emailFrom, emailTo)
ORDER BY
  COUNT(*) DESC
LIMIT 1

请看这里的小提琴.